To work very hard; do one's utmost: They like ''knocking themselves out'' for Variety
To have a splendid and exhausting time: They knocked themselves out drinking and dancing
[1936s+; perhaps fr Yiddish aroysshlogn zikh]
Idioms and Phrases with knock oneself out
knock oneself out
.
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 ]
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Enjoy yourself, have a good time, as in You're off to Europe? Knock yourself out. [ ; mid-1900s ]
Both usages allude to knocking oneself unconscious (see break one's ass