If you are unaware of the game TETRIS, then you were probably born after 2000 or never owned a classic Nokia. In either case, you surely missed out. TETRIS was a game of skill and patience, long before HALO and Assassin's Creed. This game was for real gamers.
Kerger is a programmer with some serious hardware skills, who just happened to have access to a 3D printer. Although his T-shirt is not available for purchase, it's still a fun fact knowing this piece of clothing exists.