Make fun of a learner with deadpan coarse humour (8)
I believe the answer is:
ribaldry
'coarse humour' is the definition.
(I've seen this before)
'make fun of a learner with deadpan' is the wordplay.
'make fun of' becomes 'rib' ('rib' can be a synonym of 'make fun of'**).
'learner' becomes 'l'.
'with' is a charade indicator (letters next to each other).
'deadpan' becomes 'dry'.
'rib'+'a'+'l'+'dry'='RIBALDRY'
(Other definitions for ribaldry that I've seen before include "unseemly mirth" , "Rabelaisian behaviour" , "Obscene language" , "Bawdiness" , "Coarse and disrespectful humour" .)