Insensitive Charlie, right fool! (5)
I believe the answer is:
crass
'insensitive' is the definition.
(I've seen this before)
'charlie right fool' is the wordplay.
'charlie' becomes 'c' (phonetic alphabet: alpha, bravo, charlie etc.).
'right' becomes 'r' (common abbreviation).
'fool' becomes 'ass' (ass is a kind of fool).
'c'+'r'+'ass'='CRASS'
(Other definitions for crass that I've seen before include "Grossly insensitive" , "Asinine" , "Tactless, boorish" , "'Gross, vulgar (5)'" , "Indelicate" .)