Sex and Status
This probably has as little to do with reality as the myth about males and every seven seconds, but there it is. That's how often a middle-school child will hear a homophobic slur - a sexopaulism, to coin a word.
But is it really about homosexuality? That's the question raised in the essay (and later book) "Dude, You're a Fag" by CJ Pasco. She strongly implies that at least a good portion of these slurs are not really about sexual orientation. How else to explain how a computer or object can be a "fag" (or for that matter, a movie "gay"), or that a student's refusal to use the term with actual homosexual people? The researcher also notes that there is gender component - where terms for male homosexuals are bandied about as slures, but those for female homosexuals are not.
That's because this is all about power, not sex. It's about heirarchies, and unreflective group politics. It's reminiscent of chimp heirarchies - though I rush to point out that it's immaterial for this analysis whether the driving force of that heirarchy is learned or biological; if it's the latter, there's so much socially created cruft on top that the chimp model is only useful as a framework with which to understand group dynamics.
As these adolescents are going through a process of self-discovery, they are also going through a process of determining thier "rank" in society. All sorts of social markers - and they vary from group to group, as the researcher found - serve to signal status. Ms. Pasco found herself treated differently because of her introduction as a weightlifter, or when she responded to the adolescent males as a "grownup" female rather than a peer.
In the same way, the epithet "fag" (or "gay", but with a less harsh connotation) is not a permanent category, but a brief status marker for social control in Ms. Pasco's observations. While the adolescents may not be able to articulate this in so many words, this explains why they refuse to use it with a "real" homosexual person, especially one who is older. It also explains the genderness of the epithets - in many ways, this is more of a feminist issue, than a queer issue. The temporary status of "fag" or "gay" in this context is demeaning masculinity - and simultaneoulsy reinforcing the concept of maleness being higher status than femaleness. The odd people out - at least in this study - are lesbians, but as the researcher notes, this has more to do with male fantasies of a menage-a-trois rather than lesbians per se.