Man's symbol is such rubbish — painter lacking skill primarily involved (10)
I believe the answer is:
tripartite
'man's symbol is such' is the definition.
(Isle of Man flag includes a three-legged symbol)
'rubbish painter lacking skill primarily involved' is the wordplay.
I cannot quite understand how this works, but
'skill' could be 'art' (both can mean a talent) and 'art' is located in the answer.
This may be the basis of clue (or it may be nonsense).
(Other definitions for tripartite that I've seen before include "in several sections?" , "In three sections" , "in several pieces" , "Like Henry VI" , "after a couple of cuts" .)