A way of saying "shut the fuck up", instead of actually typing it. Has less meaning than actually typing "shut the fuck up", and is often said by people that are losing an argument or can't think of a comeback.
Guy A: "You just contradicted yourself. Twice."
Guy B: "faggit"
Guy A: "Yeah, that's what I thought, you can't think of anything, loser."
Southern Tenant Farmers' Union (STFU): Large labor union, formed in Arkansas in 1934, which lobbied the federal government for better New Deal reforms. Dissolved in 1960. Commonly causes mirth among US History students who are aware of the acronym's double meaning.