Usually said to one of two people:
A. Someone who is extremely unpleasant to be around. A.K.A. a douche bag.
B. A person that is soo hideous that the only way to improve their looks is to blow their head off.
Cindy: I'll say! That bitch needs a Shotgun Face Lift.
Francis: I've got a few rounds of buckshot left in my truck. I'll be right back.