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5.
to work hard to achieve something, usually implying success
Wow, Mary! This is a great party. You really knocked yourself out.

It seems every time you give a party you really knock yourself out.
by Oneota June 11, 2008
 
1.
Equivalent to "Go for it"
"Can I have a piece of your burrito?"
"Knock yourself out."
by adhesives May 26, 2003
 
2.
A term for: Do whatever the hell you want, it doesn't bother me.
"dad, can i go to the park?"
"Can you get there yourself?"
"Yeah"
"well then, knock yourself out."
by donnald duck June 04, 2005
 
3.
Same as "go for it" or "go nuts".

If you really dont care at all about a person doing/taking something you say "knock yourself out" as in to do/eat until you pass out (if you really want to).

Same as "go for it" or "go nuts".
Person 1: "Hey man, can I have some beer?"
Person 2: "Yeah, Knock yourself out"
by Berd May 29, 2005
 
4.
to incapacitate or render oneself unconscious by means of physical, or mental, abuse or deprivation to one's own body.
"You are ridiculous. Knock yourself out now!"
"There is no way I can win this race. I might as well knock myself out!"
"I was about to kick that guy's ass for the way he was talking to my girlfriend, but he knocked himself out already."
by Fat Boy Canada October 08, 2009