AHHHHHHHHH!!! Tell them. Tell them now. Say hey billy bob, that is totally not cool and I don't want to be friends with you anymore if you continue this behavior. Or, if you have no guts (like me, i'm also bi) "can you plz stop?" I have never experienced that level of homophobia (thank the gods) but subtle things that people say in my class about being queer, I just give them the death stare. But, this is important to remember. Not all christians are homophobic. Like at all. So, don't think that, I'm not saying you are, but keep that in mind. : )