Used as an exclamation at something happening. Eg. at a hurling match when a person scores a goal in a humurous way a person can joke.
"Did ya see that, Up she flew and the cock flattened her!"
Usually in mountain gorillas, when groups come across each other in the forest, the male-male interactions are quite aggressive, involving chest-beating displays and sometimes even physical violence. Similarly, in Ireland, as a particular species of males, generally known as skangers, pass each other they display similar aggressive actions. These actions are known as throwing shapes and can involve head movements, fist movements and strange methods of walking.
Said in response to someone saying thanks. Comes from a Joke where David Hasslehoff asks a Clerk to change his name to the Hoff... when the Clerk said Sure, No Hassle. Now instead of saying "No Hassle" people just say Hoff.