knock oneself out

knock oneself out (to do something) (for someone or something)

to make a great effort to do something for someone or some group. (As if one had worked oneself into unconsciousness.) I knocked myself out to plan this party for you! She knocked herself out for us. I don't know why I knock myself out to do these things for you. You are not at all appreciative. He knocked himself out to get there on time.
See also: knock, out

knock oneself out

1. Make a great effort, as in I was knocking myself out to finish on time. This expression also is put negatively, Don't knock yourself out, meaning "don't exert yourself; it's not worth that much effort." [c. 1930]
2. Enjoy yourself, have a good time, as in You're off to Europe? Knock yourself out. [Slang; mid-1900s] Both usages allude to knocking oneself unconscious (see knock out). For a synonym see break one's ass.
See also: knock, out