Email rude comments on sergeant’s dancing (8)
I believe the answer is:
flamenco
'dancing' is the definition.
(I know that Flamenco is a type of dancing)
'email rude comments on sergeant's' is the wordplay.
'email rude comments' becomes 'flame' (flame can mean to send abuse online).
'on' is a charade indicator (letters next to each other).
'sergeant' becomes 'nco' (non-commissioned officer).
'flame'+'nco'='FLAMENCO'
(Other definitions for flamenco that I've seen before include "Gipsy dance" , "Dance from Andalusia" , "Spanish gypsy style of song and dance" , "Spanish guitar music" , "Dramatic Andalusian kind of song and dance" .)