A person who is a simpleton, a tool, or a very simple tool. From the idea of the extremely simple tool, the T-square. Also, for idea of tool squared, that is, tool to the second power, with the idea of being a super-tool. Also, t squared, T2, tsquared, or t square.
Matt: "Ted gets off on looking at pictures of farm animals."
Gus: "What a tsquare"