A person is considered matt'in it when they refuse to put a shirt on, even after being asked by a large group of people. During the shirtless time period, the person may perform physical exercises in the middle of a room such as sit-ups or push-ups and say that they have to get their work out in. Said person does not have to be fat, and is often very skinny.
Sorry guys its too hot to put my shirt on, I am matt'in it.
by big red from delaware June 20, 2009