Naughty so-and-so, say, twirling bum (5)
I believe the answer is:
cadge
'bum' is the definition.
(both can mean to beg someone for something)
'naughty so-and-so say twirling' is the wordplay.
'naughty so-and-so' becomes 'cad' (cad can mean a dishonourable person).
'say' becomes 'eg' (short for 'exempli gratia', 'for example' in Latin).
'twirling' says the letters should be written in reverse.
'eg' reversed gives 'ge'.
'cad'+'ge'='CADGE'
(Other definitions for cadge that I've seen before include "Sponge (eg money)" , "get free" , "Caged (anag.)" , "Get money by sponging" , "beg" .)