(v.) When snowboarding, skating, bmxing or similar, a 180 is turning the medium around quickly.
Both definitions are from 180 degrees, a half-turn.
B) He pulled off a 180.
This typically does not apply to Urinals or to females (unless the female likes doing #1 standing up)
Jamaal: "You know, dat bitch you said was da one fo you."
Rayshard: "That bitch? She has a small ass anyway."
Jamaal: "Sounds like a Match.com 180 to me. I tole you never git on dat thang."
Other common sentences are 90 & 120.