Another gay transguy here. I had the same problem forever. Now I usually just explain the two aspects, gender and sexual orientation, separately. Like, when I come out I tell people first that I'm a guy, and then if they ask (they usually do) I'll tell them I'm gay. But I don't give it in the same sentence, that's just too much for most people. I think it's actually a little easier for them to understand that they can't pretend to understand you (does that make any sense?) when you're a gay transguy - straight people, in my experience, have kinda stopped at that and said "Oh. Uh. Ok." I mean, they wonder why I would "choose" to not only be transsexual, but gay too - to them it's two steps down. But they have mostly said they can't pretend to understand and so they'll take it how I explain it. Whereas I know a lot of straight transguys get the "You're becoming a guy because you're ashamed to admit you're a lesbian" response because that's something the average oblivious straight person might have heard of before.
So I dunno. As with everything in life, there's a downside and an upside.
