I interpret the verse quite literally, which, in my interpretation, this is not talking about sin or anything decidedly wrong as outlined in the Word. So, if you're a vegetarian, why would I serve you meat? I would just be causing you to stumble, and that would not be showing Christ's love for each other. Think of it this way. There are things that Christians determine in everyday living that everyone - even Christians - do differently. Perhaps one Christian couple decides that they do not want to kiss until their wedding day. While *I personally* would not do that, who am I to judge and say that they are wrong for making that decision? Perhaps another Christian woman only decides to wear long skirts/dresses because they feel it's appropriate. While I may not have the same decision, I should not try to make her stumble by offering her a pair of pants. If a Christian decides not to shop at a certain store because they don't agree with the owner's beliefs, I should not try to persuade them to forgo their convictions and shop there anyway. Does that make sense?
But, I know as OCDers we may interpret this differently. I know we OCDers get caught up in "is this a sin" "is that a sin" "how do I know?" which is what I think you're really after with this question.
Remember what Paul teaches us about the law being written on our hearts:
Even Gentiles, who do not have Gods written law, show that they know his law when they instinctively obey it, even without having heard it. They demonstrate that Gods law is written in their hearts, for their own conscience and thoughts either accuse them or tell them they are doing right. Romans 2:14-15
We can trust that even if the Gentiles - who were not originally God's chosen people and therefore did not have the Law (Ten Commandments) to read - still had the Law written on their hearts. My therapist gave me some great advice once. With OCD, it's really hard to trust ourselves. We have to ignore our instinctive actions and responses to these types of thoughts and feelings. However, when a real issue comes up - we have to trust that our brains know it. I know this is counter-productive to OCD. I know how we can go around and around in our heads for hours trying to figure something out. When that happens, pray for God to give you discernment and guidance. God does not hide the truth from us; He willingly provides us with all the guidance we need in his Word.
Also, I really like what John has to say about this subject:
Dear children, let us not love with words or tongue, but with actions and in truth. This then is how we know that we belong to the truth, and how we set our hearts at rest in his presence whenever our hearts condemn us. For God is greater than our hearts (feelings), and he knows everything. 1 John 3:18-20
John goes on to say that if our hearts fail to condemn us, we can still approach God in confidence, that He will forgive us because we obey Him and remain in fellowship with Him:
Sometimes our hearts
wrongly condemn us, especially with OCD. It can be so confusing. You ask what happens when our hearts wrongly condemn us. Nothing happens. OCD really likes to use guilt - it has been said that when we encounter an OCD spike, we respond in one of four ways: anxiety (most common), anger, guilt and doubt. Guilt is only useful when we've actually done something wrong, but unfortunately for us, our guilt meter seems to be malfunctioning. It's a running joke between my husband and I that if anyone ever wants me to do anything, just make me feel guilty about it!

So if we are confused about whether we have sinned or not, or whether or not that OCD thought was a sin or not, we have a backup plan for when we are confused.
We have someone to come to our defense: Jesus.
My dear children, I am writing this to you so that you will not sin. But if anyone does sin, we have an advocate who pleads our case before the Father. He is Jesus Christ, the one who is truly righteous. He himself is the sacrifice that atones for our sinsand not only our sins but the sins of all the world. - 1 John 2
So, let's break down all of this information.
- We know that we are made alive in Christ and the Law is written on our hearts. Therefore, we have no excuse for sins.
- But because we have been saved, our hearts (conscience/Holy Spirit) condemn us when we do sin.
- Sometimes, our hearts fail to condemn us. When that happens, we have Jesus to intercede for us on our behalf.
- We also know that God is greater than our feelings, especially when our hearts wrongly condemn us - as it often does with OCD.
So, it appears as though our bases are covered here. Now, at the heart of your question, what you're really asking is, how do we know what's real, and what is OCD?
I really only have one answer for that: if you think it might be OCD, it's OCD. If it walks like OCD, talks like OCD, acts like OCD, we can safely assume it's OCD. And even if we wrongly identify something as OCD (our hearts fail to condemn us), Jesus still intercedes for us on our behalf.
I hope this makes sense. It's hard for us Christians because we have such different standards than the rest of the world. Hang in there.