also: きにすんな
never mind!; don't worry about it
Casual imperative used to tell someone not to be concerned or bothered. The contracted form 気にすんな is even more informal.
Don't worry about it even if you fail.
I said don't worry. It's fine.
Negative imperative form of 気にする (to mind, to worry). The contracted form 気にすんな comes from casual speech contraction of するな to すんな.