b-shirt Share definition Flag A t-shirt you get free when every you buy a case of beer. Usually given away as a promotion. Frat Guy One: Hey, did you get the beer? Frat Guy Two: Yah, and a free b-shirt to go with it. b-shirt by ThePsychoMachine March 4, 2009 0 0 Get merch Get the b-shirt mug. Buy Now — $32.95 See more merch