Rotten fellow, say, flipping bum (5)
I believe the answer is:
cadge
'bum' is the definition.
(both can mean to beg someone for something)
'rotten fellow say flipping' is the wordplay.
'rotten fellow' becomes 'cad' (a cad is a dishonourable person).
'say' becomes 'eg' (both can mean 'for example').
'flipping' shows that the letters should be reversed in order.
'eg' written backwards gives 'ge'.
'cad'+'ge'='CADGE'
(Other definitions for cadge that I've seen before include "Go about begging, scrounge" , "Get money by sponging" , "Caged (anag.)" , "Scrouge, ask for" , "Try to get (something) without paying" .)