Not being polite to a bird! (5)
I believe the answer is:
capon
'bird' is the definition.
(capon is a kind of bird)
'not being polite' is the wordplay.
I cannot really understand how this works, but
'not' could be 'o' (I've seen this in other clues) and 'o' is found within the answer.
The remaining letters 'capn' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'to a' acts as a link.
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" .)