To do something useless or futile...something that is not going to get you anywhere or help you make progress?
Quite close, to spit into your chin or beard means to immensely regret sth you have done or even more popularly, sth you haven`t.
This idiom perfectly describes my feelings now. I bought 12 items, one of which was faulty, at a popular auction site. After a futile attempt to resolve the matter with the seller, I gave him one negative comment and 11 positive ones. He is answering back with 12 negative comments into my auction account. Can you believe it?
I should have given him one negative and wait to see what happens, but I wanted to be fair, as usual. Fairness is my second name, sort of. Now I am spitting into my chin.