look up any word, like cleveland steamer:
 
2.
The obnoxious look on the face of one who beleives that his/her shit does not stink. Also known as a "shit eating grin."
"How dare you stand there with that smug mug, while the stench of your flatulence makes my eyes tear up!"
by Michael Vincent March 11, 2009
 
1.
The action of collecing sweat on the pawn of the hand from a person's crotch. After collecting the sweat then wiping it in their partner's face.
Thats quite a smug mug you got.
by zacher November 16, 2006