Fool's bet

A bet in which only a fool would take; one that someone is guaranteed to win.

Peep1: How much you wanna bet that he's gonna make the next basket?
Peep2: that's a fool's bet!
Basketball player: *makes a basket*
Peep2: See?! Fool's bet.
Peep1: Aw man. I thought you'd be dumb enough to fall for it. There goes my easy money...