Not being polite to a bird! (5)
I believe the answer is:
capon
'bird' is the definition.
(capon is a kind of bird)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for capon that I've seen before include "Castrated fowl, for eating" , "Male fowl fattened for eating" , "one fattened specially" , "A tasty bird" , "Emasculated fowl" .)