I would say that "You" is being used here to mean "One" or "People".
"One likes either guys or one likes girls."
However, I will concede that actually that statement only suggests that the speaker is someone who doesn't understand/approve of bisexuality.
Of course. But aside from that, the statement "Some people say that they don't understand homosexuality: You either like girls or you like guys" still doesn't make much sense. Whether you're a girl or a guy, liking girls or guys doesn't speak to the issue of understanding homosexuality. The first half of the statement raises the issue of understanding homosexuality, but the second half doesn't speak to the issue. Most people like either girls or guys, regardless of whether they understand homosexuality.
So I'm suggesting that the statement doesn't say whatever it is the writer is trying to convey. If I were an editor, I'd ask for clarification. I just can't tell what Batman means.
In BrE, we frequently refer to the two sexes as "guys and girls" (maybe guys and gals!) rather than "men and women". Many lesbians refer to themselves as "a girl who likes girls", regardless of their age.
Americans do, too, all the time. It's very conversational, and that's not necessarilty bad.
I just want Batman to know that it's a little sloppy and sometimes offends. Many American women dislike being called girls because they feel it takes away their adulthood, especially at work. At the American university that I went to, it would have been treated as a writing mistake. Girls and guys is worse than girls and boys because there isn't even parity: girls are young, guys are any age.
