Hi there!
Im a Christian with Aspergers, and I think I can help. I used to have this same bitterness, and I know exactly where it comes from: your friend has a love deficit. He cant give love unless he RECEIVES love firstGods love, of course.
I want to say thank you and congratulations for putting up with this person and his anger. Looking back, I wonder just how so many people were able to put with me. THAT was a miracle, and it was one that took a very long time for me to appreciate. If you can get him to change, I promise you your reward will be great. There are so many benefits to having a person with Aspergers as a friend.
For people with ASsome of us call ourselves Aspies, so Ill use that term heresocial interaction rules just dont come naturally, as you know. This, as you can expect, leads to messing up social situations all the time. And this, in turn, leads to social isolation. We get very lonely and bitter.
We feel like everyone in the world is against us, and we just hate how people are able to go on with their happy lives and not notice our own suffering. And for a long time we Aspies couldnt get a diagnosis, so we had no idea what to do. We knew we were suffering, but we couldnt tell people; we thought theyd just ignore us or say that we should just straighten out.
Our brains are wired to feel negative emotions very strongly, and thats why the slightest things will set us off sometimes. It does get controlled with age, but at a much slower rate than regular people. I can remember my parents constantly telling me that I was actin like a two year old! It got so annoying hearing that over and over, but it was true.
But the anger comes from social rejection. Your friend, as you can obviously tell, had difficulty fitting in and as a result came to think that the world was against him, and that it was harsh place full of mean people. Thats how I used to think. I described my life as a living Hell all the time.
Not every person with Aspergers is angry like your friend is; if this was true then the DSM would list being angry as an Aspergers trait. Its not that were all angry; we just have difficulty controlling our emotions, and since the world doesnt make sense to us, a lot of things in the world just seem wrong. And we cant just sit there KNOWING that somewhere, someone is doing something wrong, especially if its being done to us.
His failed social interaction left him alone and isolated, and he chose to react to this by being angry and hating the world. It was a choice he made to become angry, even though it might have been a subconscious choice. I know because not every person with Aspergers is angry like that; not even I could be perpetually angry. Some of us respond to our social isolation (it tends to be inevitable) in other ways. Some of us come to actually embrace it! But not everyone can do that.
I felt worthless, alone, worried about my future, and misunderstood. I technically believed in God, but my words and actions and the cynicism with which I viewed the world indicated otherwise. It wasnt all bad, but a lot of the time I spent dwelling on negative thoughts could have been spent on making friends and just being a nice person.
My problem was that I was taking on the world alone. I thought that it was just me vs. everyone else, the misunderstanding people that didnt realize that I had Aspergers and would say what I wanted to, when I wanted to, and I didnt care for their social stuff. I didnt want to be overdosed on happiness like them, and I didnt want to care for anyone else. Why should I care for others, I thought, When no one has cared for me?
The truth was that people DID care for me. Plenty of people recognized my natural intelligence and love of learning and my ideas, and they appreciated my sense of humor (even though I was basically humiliating myself sometimes). But I couldnt see them the way they saw me, and I certainly couldnt see myself the way they saw me.
Him calling you selfish for working at a camp and hating things like babies sounds a lot like the way I used to be. I also had that whole I wish everybody could die except me, because they deserve it! People all hate each other, theres nothing wrong with me doing it!
That kind of thinking comes from a human-centered worldview, the kind I had. Your friend can claim hes a Christian all he wants, but he obviously isnt one.
The way I got out of this cant exactly be repeated by every other individual with AS (although I sure wish it could!) but this situation your friend is in is VERY similar to what I went through as a teen (but I got out of it at a younger age while evidently hes still in it, although it was through no fault of my own). I cant leave an Aspie brother behind to face battles he (or she) cant win alone, the way I tried to.
Heres what you need to do:
Start a Bible study with him. It has to be one-on-one. Answer every typical skeptics question about the Bible that hell come up with, and show him that Christianity is indeed substantial and logical. Show him that it makes sense. Get other Christians to help you with this if you need to. I, for one, know a couple of things in the Bible that I can filter through the autistic mind on your behalf, so if you need suggestions I can give some.
Let him trust you and find nothing to hate about you. You might think this is tough on your part, but even if you have some flaw he can see through (that he thinks you have), if youre as kind to him as you can be then hell look past that flaw, knowing that youre a very valuable friend to have. Even when I was mean and bitter I made it a point to value my friends, even though I dont think I ever really communicated this to them well.
Let him know that you are genuine, with no ill intentions. Explain your motivations to him, tell him how you see him. We autistic people arent good at seeing things outside of our perspective, but its not that we cant do it at all; its just that we dont really know WHEN to do it. Let him give you his point of view, how he sees the world, and you open up to him in return. Because we cant pick up on other peoples social cues and non-verbal communication, we gain a lot from peoples words because thats all we can read. Because no one would just straight up open to me, I felt like people were one-dimensionallike I was in a world of fictional characters and I was the only real person aside from my brother who also had AS. Tell him verbally how you feel and how you think. Dont assume that he can just figure it out, because he honestly cant unless he knows where to begin. If youre his friend, then hopefully opening up to him shouldnt be too hard. Be vague if you have to, and dont feel like you have to surrender your personal problems. Just say enough to let him know that youre a human being, just like him. Only ONE non-Aspergers person has really done that with me, and as a result, shes a great friend even though we live far away from each other and we just email each other.
Be honest with him and his sin. Explain to him how his anger and hatred is destructive, and let him know that he doesnt have to be that way. You dont have to mention Jesus, but you do need to explain to him about his fallen nature. Something to make him realize that he needs help, not the rest of the world. But make sure you emphasize that its not his condition thats wrong with him; its how hes handling it.
Get him back on that medicine.
Give him the chance to cry out to God. It took me a long time to realize that the problem was not with the world; it was with myself. Obviously, your friend wont get it if you just straight up say that to him, but its the truth. Humanity and the world is fallen, and we can either sit around and mope about it or we can find the good in the world and work to undo the damage of the evil and misery. Thats what Id love to help you do with your friend. Once he cries out to God and realizes that even though he is an angry, bitter person with so much hatred in his heart, God loves himall he had to do was accept that he was the sinner.
But let me tell you just how it works, what happens when a person with Aspergers comes to Christ. Its a wonderful, cathartic experience that I really cant talk about without my eyes getting watery. I like to call it the perfect hug.
As you probably know already, autistic people dont like being touched, and some of us dont like the feel of certain clothes or textures. Were just very sensitive about that, although for me personally its not too bad. But with hugs, we can be very sensitive. Even now I have relatives that want to hug me for some reason and I sort of go limp if Im on the receiving end.
A perfect hug isnt a literal hug; its a hug that conveys all of the affection and love without the unwanted stimulation. Its the kind of hug that says, I know that the world is a harsh and scary place, but I love you, even though youre different. I want to protect you and make you feel better.

That kind of hug can only come from Gods love.
I cant remember the exact chapter and verse, but somewhere in 1 Corinthians Paul talks about how if he could do all sorts of cool things but not love, then hed be worthless. And in 1 John somewhere (again, I suck at chapter and verse references on the spot, sorry): We love because he first loved us. That is very true with people with Aspergers. Its not that we cant literally love someone, but let me tell you, before I felt Gods lovebefore he told me that I was loved and valued despite all of my social problems and attitude and mannerismsI began to feel love for others. I WANTED to love other people so much more, to make up for how selfish I used to be.
Because we autistic people have difficulty perceiving the world outside of our own lenses, we sometimes end up being a bit selfish without meaning to. It isnt until after we make some mistake and act like a jerk and get punished for our actions that we realize how bad weve been.
There are ways to make him manage his anger and make him less upset and reactionary that dont involve the Bible, but the most effective way to help him is to let him know that Christ died for people like him.
Jesus was bullied, He was blunt with people who were doing things wrong, He never lied, He hated hypocrisy, He had to live in a world that operated differently from how His perfect, sinless brain worked, He had people misunderstand Him, He felt lonely sometimes, He was tempted to act superior to everyone else (some of us people with Aspergers feel like were always right or were smarter than everyone else), but He didnt do it. Jesus didnt have Aspergers, obviously, but His struggles were similar enough. During Jesus lifetime, He went through every struggle imaginable, every struggle that human beings can have, either directly or indirectlyand He did it all so that we wouldnt have to. And yet we still do because often we dont recognize that theres a way out.
He might already technically know the story, but it obviously hasnt hit home yet. When a person becomes a genuine Christian like I did, theres a big difference. They wont be perfect, but theyll change.
I think then your friend will realize that he needs to change his ways, and he will need your help. Youll have to teach him all the social rules and how to see the world and everything in it with joy instead of bitterness. Sometimes I have trouble with this, but I know that Christ inside me. I cant give up on life because I know that I am becoming more social for Gods sake, not my own survival. Im not trying to cure myself of my Aspergers, because I dont need curing, but I do want to improve myself and show people that I have value, just like all human beings do.
Ill be sure to pray for you and your friend.

Feel free to ask me anything if you dont understand something or need more information. God bless, and dont give up on your friend! God can free him from his misery!