The act of not having the sense to admitting one's deficiencies in something right after proving that one is deficient.
-"No man, I'm awesome. It was just the wind, I'll score the next goal."
-"Dude, don't pull a uni..."
If you act like a player in front of your friends, then freeze up when talking with a chick, then brag to your friends about what a player you are later that night then you just pulled a uni.