The concept made popular by Mike "The Situation", from the popular reality show, "The Jersey Shore".
The concept, as defined by The Situation: "We have an abundance of wife beaters ... we wear before we go out. Then it's T-shirt time. Right before we go out we take off the tank and then we put on our fresh shirt."
Jenny: Yo, you ready to go out yet?
Newton: Not Yet, I still got my wife beater on. It ain't T-Shirt Time yet.