Tyto is correct.
But if you REALLY want a good comeback ... Ask them "Why do you keep bringing this up, obsessively? Is it because you wish YOU could have sex with me? Well, that's not gonna happen." And then just walk away.
what's a good comeback to someone always making fun of u saying u have sex with someone when u don't i can't think of anything to say back and every time i just shake my head to whatever they say but i rly wanna cool comeback he says it every day?