I’ll eat my hat.

我敢打赌…绝对不可能发生，要是…发生我把头给你
e.g. If she actually marries him I’ll eat my hat.
她要是真的会嫁给他，我就把脑袋给你。
I’ll say! 当然！确定！
e.g. Does Xiaojiang eat a lot? 小酱吃得很多吗？-I’ll say! 当然!

wear many hats 身兼数职

e.g. Xiaojiang wears many hats: she’s a doctor, a musician, and a writer.
小酱身兼数职：她是医生、音乐家和作家。

white hat 正直的好人

e.g.We work for the good guys. We’re the white hats.
我们为好人工作。我们是正直的好人。

talk through your hat 信口开河，随口乱说

e.g. Nothing of what he said made sense, he was talking through his hat.
他说的话没一点道理，他只是随口乱说。