The act of editing players and teams on your brand new sports video game (NCAA Football 09, NBA Live 2K9, Madden 09, etc.) and making every single attribute, of every single player on your favorite team, a perfect 99. Performed by a 99er.
Billy: I just got the new madden! Wanna come over and play me?
Tom: No way! I know you spent all night 99ing the steelers!