Used to describe someone who is being a cock, possibly inadvertently or by accident, and normally used by much bigger cocks/jerks, who incorperate the phrase into a petty rant against the normally helpless first party. Often used in description of first person to a third party, with all three present (see example).
1: Look, I'm sorry. It's not my fault, I -
2: Oh no, you forget it, sonny! You're too busy prancing about on your boat to give a fuck for us lowly workers!
3: Whats the crack here then, lads?
2: Oh the office party has only been bloody cancelled, hasn't it! And our man Flint here isn't even sorry! Prick.