Man, that's a tough situation. Being a conservative Christian on a very liberal urban campus has landed me in a ton of these kinds of problems. I usually find that if I voice my complaints without being angry or accusatory that the others in the situation are very understanding & accommodating.
For example: I didn't drink until I turned 21. My roommates all drank & we regularly had parties at our place. Just about every weekend, I'd end up having this conversation:
Friend: "Hey man, you wanna beer?"
Me: "No thanks, dude, I dont' drink."
Friend: "Wha..Why not?"
Me: "Cause I'm not 21."
Friend: "Yeah, well so what, there's no cops here!"
Me: "Yeah, but that's what the law is, so that's what I'm gonna do."
Friend: "Yeah, but the law's not fair! I mean, we can vote or go in the Army & get shot at 18!"
Me: "Hey, man, I'd love to be allowed to drink at 18, but that's not the law."
Friend: "Well if you wanna drink then why don't you?"
Me: "Well, because the Bible says that we're to respect the government that God has placed in power over us & so, as a Christian, I believe I need to respect the drinking age."
Friend: "O, the Bible, huh? So I guess you thin we're all a bunch of sinners, huh?"
Me: "Well, yeah, but that includes me. I mean, just 'cause I don't drink doesn't mean I'm perfect. I'm just as sinful as anyone else around."
Surprisingly, I got to share my faith a lot
because of my decision to wait for 21. I'm not sure how many of my friends remember
my testimony, but hey: I gave it any how!!