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1.
That funny look a man, or woman gets on their face when an intimate subject is brought up, usually something sexual. Often accompanied with the phrase "I dont know what you are talking about."
Teen 1: "Did you see Dad's sex smirk on his face when Mom said something about going on their first camping trip?"
Teen 2: "Yep, I puked in the back of my mouth a little."
by MoreThanLust December 13, 2011
 
2.
1. An involuntary smile that is the direct result of recent sex.

2. A grin that appears when your friends start talking about sex and they don't know that you've done it recently or ever.
Dude, what is with that Sex Smirk? The only girl you've seen all weekend is my sister...
by Prolemthas June 16, 2011