Up or down, it is unacceptable (3,2)
I believe the answer is:
not on
I believe this is a double definition.
'up or down' is the first definition.
'unacceptable' is the second definition.
(something 'not on' is unacceptable or frowned upon)
'it is' is the link.
(Other definitions for not on that I've seen before include "Informally, can't be accepted or tolerated" , "Out of the question" , "Colloquially, cannot be tolerated or accepted" , "Modern phrase for unacceptable" , "Definitely inadvisable" .)