a son of a gun
1. (American informal) a man who is unpleasant or who has made you angry He's one mean son of gun - so be careful around him.
2. (American & Australian informal) if you call a man or a boy a son of a gun, it is a way of showing affection for them The little son of a gun has done it again - he's won all his races.
3. (American informal) a way of referring to an object which is causing problems for you or making you angry The computer's crashed and I don't know how to get the son of a gun working again.