Basic Trope: Someone claims they don't have some skill, but when the chips are down, it turns out they do.
Straight: Alice and Bob are at prom night, and Alice thinks Bob can't dance. He leads her onto the floor and dances like a champ. Upon being confronted about this, he says "I Lied".
Exaggerated: After prom, Alice and Bob go back to a motel room and have fantastic sex - despite Bob claiming he has no idea what to do in bed. After that, they wake up the next morning and Bob makes her a five-star breakfast despite claiming he can't cook...
Downplayed: Alice and Bob go out on the dance floor. He can't dance particularly well, but he dances better than Alice thought.