The fact that Jenny is raped while unconscious during the course of the film shows that Jenny may not be aware of all of the sexual encounters she's had.  She may have been raped before, and so her claim that she had only ever had sex with Telly may be false (without her even being aware that it's false.)  I always thought that was the whole point of the rape scene — to show that naive beliefs held by these kids can't be trusted.  Telly's belief that he's only ever slept with virgins is probably false (unless he slept with a virgin who had contracted HIV some other way) and so is Jenny's belief that Telly was her only partner, or that in a culture of random drugged-out sex and casual rape anybody can even be sure who they've slept with.  I've modified the article accordingly.