Doug's 2 cents:
It shouldn't be up to us to label another person's sexual orientation.
If someone feels they are more attracted to the same sex, and they want to call themselves gay, then go for it.
If they feel equally attracted to both sexes and want to be "labeled" bi, then that's up to them.
If they're more attracted to the opposite sex, then they can call themselves straight.
I know that I like the ladies, I "know" that I'm straight. In other words, even if anal stimulation were to arouse me (given or received), the idea of anal stimulation to/from another man disgusts me. Yes, a mouth my be a mouth, but the idea of kissing another man is unappealing.
It's all in the mind.