Hahaha - oh so true. I just explain that we're a Church as old as the Catholics, and that's usually enough. It's not all that precise, but it's a good ten second explanation - it takes significantly longer if they want more than that!
I'm about to spend a week working in mission in my grandmother's country town with an ecumenical, largely evangelical group, teaching Bible stories and christianity to kids (well, mostly kids). It should be fun, and yes I have my SF's blessing (he figures I can teach the kids the Orthodox stuff...and yes, I can) but I am expecting lots of similar questions over the next week, just more respectful - they'll accept me being Christian since I've been accepted onto the team
I went to this when I was growing up (it's been going on for a very long time) and my friend who I've known since before we were born (our parents have been friends since college) is one of the people running it and he's been asking me to help for years, so I'm doing it. I'm very much looking forward to it!