1.) When someone completely soaks their white t-shirt to the point that it becomes see-through.
2.) A direct result of overactive perspiration in an embarrassing public setting.
Dude 1: Hey bro, that was an intense game of b-ball
Dude 2: Fuckin' right dude, I'm totally rockin' a Sweat T Shirt Contest right now.
Dude1: Fuckin' gross, man!