About to get impolite and coarse (5)
I believe the answer is:
crude
'coarse' is the definition.
(synonyms)
'about to get impolite' is the wordplay.
'about' becomes 'c' (abbreviation for circa).
'to get' means one lot of letters go next to another.
'impolite' becomes 'rude' (similar in meaning).
'c'+'rude'='CRUDE'
'and' is the link.
(Other definitions for crude that I've seen before include "Lacking refinement" , "Not refined, like oil" , "In a natural state - vulgar" , "Tasteless, not refined" , "Not expertly made" .)