[Comedic trope] Character denies existence or possibility of something, is immediately proven wrong.
Princess Bride - Wesley denies the existence of ROUSes and is instantly attacked by one.
UP - Russell shows off his GPS and says they’ll never get lost, and immediately drops it out the window.
Spongebob - Squidward ridicules Spongebob and Patrick for sitting around doing nothing, as though a picnic is just going to fall right out of the sky. Cue a picnic falling out of sky.
Road to El Dorado - Miguel and Tulio, posing as gods, are forced to play a game where you hip-bounce a ball into a hoop high on the wall. Tulio whispers to Miguel that the game is impossible, and the opposing team immediately and easily scores a point.
Megamind - He is sure Roxanne won't figure out where the secret entrance is. Cue her noticing a doormat that says "Secret Entrance" and entering through the holographic wall.
Moana - Tui tells the children that there "There are no monsters!" But then he accidentally touches a scroll, which unfurls and sets off a domino effect of all the hangings dropping open, all featuring painted monsters. Children scream, cry, throw up.
Tangled - Rapunzel smugly informs a captive Flynn that she has hidden his bag where he’ll never find it. He casually glances around and nods toward the pot where the satchel is.