I paused at the T-shirt gun reference myself, then realized after a moment that I knew what it meant and that I have seen them in action. At baseball games, they give out free T-shirts between innings. The T-shirt gun allows them to fire the shirts high into the stands -- whoever catches one gets a free shirt -- rather than just handing them to the rows within throwing distance.
At first I thought, would that be some kind of gun designed to fit into the pocket of a T-shirt?
And you'd think I'd know my gun terminology, as an American!