knock yourself out = please begin doing it
Ex. If you want to make hotel and airline and car reservations and take care of everything, well, then, knock yourself out.
A friend is staying with me for the moment and one of his favourite idioms is “Knock yourself out!”
I know that I should not take this literally but that’s what my brain does!
Last week, I fell on the gravel path during my regular run… I knocked myself out!
This week, I fell from my push bike… I knocked myself out!
Some words are so powerful aren’t they!?
So… I have asked him to avoid saying “Knock yourself out!” I rather stay alive and in good health 🙂
Roseline Deleu
www.fengshuisteps.com.au
Feng Shui Steps 
Good point! Words can have power – and you are aware enough to see it happen. Imagine what power (ours included) can have to either hinder, help, or heal, especially for those just coming to that kind of awareness? Excellent reminder for all of us – thanks for posting this 🙂
One day I also had someone saying “Break a leg!” as I was walking to the stage to do a presentation in front of a very large audience