bet one's boots

[bet one's boots] or [bet one's bottom dollar] or [bet one's shirt] {v. phr.}, {informal} 1. To bet all you have.

This horse will win. I would bet my bottom dollar on it.

Jim said he would bet his boots that he would pass the examination.

2. or [bet one's life]. To feel very sure; have no doubt.

Was I scared when I saw the bull running at me? You bet your life I was!