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 more definition
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