Less civil (5)
'less civil' is the definition.
('rude' can be the opposite of 'civil' so perhaps 'ruder' is reasonable for 'less civil')
This is the entire clue.
(Other definitions for ruder that I've seen before include "More impudent" , "Less civil" , "With less warning, perhaps" , "less pleasant in manner" , "More vulgar" .)
(Other definitions for meaner that I've seen before include "More miserly" , "Rename as being more stingy" , "Less generous" , "More stingy or parsimonious" , "Rename (anag.)" .)