It's a rather pathetic defense mechanism for men who are no good at sex. It's rather like the tactic of insulting yourself in grade school, because if someone else does after you have it's okay and you still win. If you build a sexual fantasy around being bad at sex and having a "girlfriend" who's not really your girlfriend at all but has sex with anything possible in front of you or before telling you about it, you're the greatest gift any slut could have, you actively recruit men for her to have sex with, while pretending to be turned on when she won't have sex with you, but you provide all the benefits of a real boyfriend.
