shit-grinning

(adv.) an overt display of self-satisfied smugness when clearly such displays are either undeserved or unwarranted. As if the subject were to smile innocently only to reveal a mouthful of shit to his/her peers.

Kyle: "Did you see that shit-grinning bastard John after he got his paper back?"

Whitt: "Yea he looked like a gloating douche for sure"