The alias one goes by at parties to avoid tarnishing their real name through any of various embarassing actions one often performs at parties. In essence this helps to make sure that "What happens in the party, stays in the party."
(Day After Party)
Partier: Hey bro that was an awesome party last nite. Man insert name here got really fucked up!!!
Friend (host of party): I didn't invite anyone named insert name here
Partier: Oh well that must've been his party name.