Homophobia is a fear of gay people (homophobic means to be scared of people who are atracted to those of the same sex). Usually people may be or act homophobic because in many teenage groups you are either for or against a subject. So if you don't hate gay, you are seen as gay. This leads to many people becoming homophobic because it is shuned and considered wrong to the public.
Man 1: Did you see that guy. He is such a gay!
Man 2: So who cares... it's not like I'm homophobic.
Man 1:.. umm.. What? You sound like a gay man.
Man 2:Ohh sorry, I mean. Gays discust me. It's just wrong.