knock oneself outidiom
Definition of knock oneself out
1 : to cause oneself to become unconscious He hit his head against the table when he fell and knocked himself out.
2 informal : to make oneself very tired by doing work I knocked myself out to get the job done on time.
3 US —used to tell someone to go ahead and do something "Do you mind if I use this exercise machine first?" "Knock yourself out."