Don't mention it in any way, shape or form! (3,2,3)
I believe the answer is:
not at all
'don't mention it' is the definition.
(I've seen this before)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for not at all that I've seen before include "You're welcome" , "My pleasure" , "denial" , "acceptance of apology" , "By no means - polite disclaimer" .)