Negative rubbish, everything - don't mention it (3,2,3)
I believe the answer is:
not at all
'don't mention it' is the definition.
(both can mean 'you're welcome')
'negative rubbish everything' is the wordplay.
'negative' becomes 'no' (no is a kind of negative).
'rubbish' becomes 'tat' (tat can mean rubbish or poor-quality material).
'everything' becomes 'all' (all things).
'no'+'tat'+'all'='NOT AT ALL'
(Other definitions for not at all that I've seen before include "denial" , "forget it" , "My pleasure" , "By no means - polite disclaimer" , "Anything but!" .)