other uses: often used to refer to sack (of any size) costing $20. and sometimes to refer to a 20 dollar bill.
Girl 2: The one with the acne, hiking backpack, and no social skills?
Girl 1: Yeah. He's in my psych class. He's such a Twamp.
Origins may be from TWAT + SWAMP = TWAMP, or supposedly a reference to some sort of mold growing there. They always throw down Wednesday nights, and you'll be sure to see lots of freshmen sluts wasted out of their minds. An experience everyone must have at least once.
Person 2: Nah, I don't want an STD.