Gross; stupid (5)
I believe the answer is:
crass
I believe this clue is a double definition.
'gross' is the first definition.
(I've seen this before)
'stupid' is the second definition.
(I've seen this before)
(Other definitions for crass that I've seen before include "Tactless, boorish" , "Boorish about scars" , "Unrefined" , "Showing gross lack of sensitivity" , "Blundering" .)