I'll eat my hat
US /aɪl iːt maɪ hæt/
UK /aɪl iːt maɪ hæt/
1.
used to say that you will be very surprised if something happens, because you think it is impossible
:
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If he actually finishes that project on time, I'll eat my hat!
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You think she'll apologize? I'll eat my hat if she does!