100 are less polite, and altogether coarser (6)
I believe the answer is:
cruder
'coarser' is the definition.
('crude' can be a synonym of 'coarse')
'100 are less polite' is the wordplay.
'100' becomes 'C' (Roman numeral).
'are less polite' becomes 'ruder' ('rude' can be the opposite of 'polite' so perhaps 'ruder' is reasonable for 'less polite').
'c'+'ruder'='CRUDER'
'and altogether' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for cruder that I've seen before include "Less refined, more vulgar" , "Less refined, more primitive" .)