Insensitive as car crashes against ship (5)
I believe the answer is:
crass
'insensitive' is the definition.
(a crass comment might be insensitive)
'car crashes against ship' is the wordplay.
'crashes' is an anagram indicator.
'against' says to put letters next to each other.
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'car' anagrammed gives 'cra'.
'cra'+'ss'='CRASS'
'as' is the link.
(Other definitions for crass that I've seen before include "Coarse" , "Showing gross lack of sensitivity" , "Grossly insensitive" , "Asinine" , "'Gross, vulgar (5)'" .)