Rows in church? That's vulgar (6)
I believe the answer is:
coarse
'that's vulgar' is the definition.
(synonyms)
'rows in church?' is the wordplay.
'rows' becomes 'oars' (I've seen this before).
'in' means one lot of letters goes inside another.
'church?' becomes 'CE' (abbreviation for Church of England).
'oars' inserted into 'ce' is 'COARSE'.
(Other definitions for coarse that I've seen before include "Rough or rude" , "Rough to the touch or lacking refinement" , "Rough in texture, or vulgar" , "Inferior" , "Rough or crude, lacking refinement" .)