I have this happen to me at times ... dunno why ...
Meaning[]
It means for a plan to go wrong or something to be broken! It is not good news if something's been knocked on the head.
Use in Normal Speech[]
When something's gone wrong.
"Oh pants! That's the trip knocked on the head - I've had a heart scare!"
When something just won't work.
"Boom. Innacurate nickname! That's knocked that on the head - unless ... "