eat one's hat

A humorous action that one will allegedly take if something very unlikely happens. Kevin is always late, so if he actually shows up on time, I'll eat my hat.

An expression describing the hypothetical act of penance that one promises to take if they are wrong about something. I'll eat my hat if the repairs end up costing less than $1,000. If you can prove me wrong, I'll eat my hat.

Fig. I will be very surprised. (Used to express strong disbelief in something.) If Joe really joins the Army, I'll eat my hat. If this car gives you any trouble, I'll eat my hat.

Declare one's certainty that something will not happen or is untrue. This hyperbolic expression almost always follows an if-clause, as in If he's on time, I'll eat my hat, that is, "I'll consume my headgear if I'm wrong." Charles Dickens used it in Pickwick Papers (1837): "If I knew as little of life as that, I'd eat my hat and swallow the buckle whole." [First half of 1800s]

To declare one’s readiness to consume one’s headgear if a statement should prove false, an event should not occur, and so on. The likelihood of actually doing so is presumably very remote, which is the very analogy being drawn (to a statement’s being false, an event not occurring, and so on). The expression appeared in Dickens’s Pickwick Papers (1836), in the words of one clerical gentleman, “Well if I knew as little of life as that, I’d eat my hat and swallow the buckle whole.”