I’ll eat my hat
Definition 1 of 1
Pro Tip 1/3Implied Consequence
The phrase suggests a humorous or hyperbolic consequence for a wrong prediction. 
If this team wins, I'll eat my hat.
Pro Tip 2/3Unlikely Scenario
The expression is often used when the speaker believes an event is highly improbable. 
If she ever decides to skydive, I'll eat my hat.
Pro Tip 3/3Not Literal
It's not meant to be taken literally; it's not a real promise to eat a hat. 
He said he'll eat his hat if it rains today—it's just an expression.