Party enforcing six-pack ban? Impossible (2,3,2)
I believe the answer is:
no can do
'impossible' is the definition.
('no can do' can mean something is impossible)
'party enforcing six-pack ban?' is the wordplay.
I cannot quite see how this works, but
'party' could be 'do' (do is a kind of party) and 'do' is present in the answer.
This explanation may well be incorrect...
(Other definitions for no can do that I've seen before include "Absolutely not!" , "off-putting response" , "Impossible, I'm afraid!" , "That's not possible" , "Can't manage it, see doc anon" .)