Man sees partying all together (2,5)
I believe the answer is:
en masse
'all together' is the definition.
(I've seen this in another clue)
'man sees partying' is the wordplay.
'partying' indicates anagramming the letters.
'man'+'sees'='mansees'
'mansees' is an anagram of 'EN MASSE'.
(Other definitions for en masse that I've seen before include "As a body (Fr.)" , "In force" , "in concert" , "All together (Fr.)" , "Many as one" .)