Named after the short but tenacious Syracuse point guard Gerry McNamara, a GMac is any inprobable clutch or momentous action a person pulls off, usually at the last second.
I can't believe Tom pulled that test grade out of his ass -- that was a total GMac.
a gaysha person who wishes he was chris brown. has a chode, has small arms, and has no game at all. only gets guys, not girls. gives blumpkins, and loves to give an alabama hot pocket.
yo look, its gmac