That guy is one who attends a party only to take advantage someone's drunk girlfriend. Now not only did you ruin her life, but you also pissed off her boyfriend likewise all for your own greed. Perhaps this can be a tactic for vengeance, perhaps you are just a douchebag. Whatever the case, you are now "that guy"
Hungover college student: OMG OMG OMG, I totally shouldn't have slept with "that guy" last night! What if my boyfriend finds out? He'll probably beat me and none of it was even my fault!