Tease lad about being coarse (6)
I believe the answer is:
ribald
'coarse' is the definition.
(both can mean vulgar)
'tease lad about' is the wordplay.
'tease' becomes 'rib' (rib can mean to tease or mock).
'about' indicates anagramming the letters.
'lad' with letters rearranged gives 'ald'.
'rib'+'ald'='RIBALD'
'being' is the link.
(Other definitions for ribald that I've seen before include "Coarsely mocking" , "Indecent" , "Humourous in vulgar way" , "Coarse" , "Coarsely humorous; scurrilous" .)