Word used in bleak situations, normally when one has made a serious faux-pas or is rethinking an embarrassing situation. Not as overt as a swear word but just as potent when muttered under your breath while walking at a quick pace, or blurted out (torrets style) when you are re-living an awkward situation in your head. Also good to shout when you painfully stub a toe or bang a funny bone against something hard.

A casual invitation / threat used by an individual that is not afraid of fucking someone up.