To trespass with intent — not half impolite! (7)
I believe the answer is:
intrude
'to trespass' is the definition.
('intrude' can be a synonym of 'trespass')
'with intent not half impolite' is the wordplay.
'with' is a charade indicator (letters next to each other).
'not half' suggests halving the letters.
'impolite' becomes 'rude' (similar in meaning).
'intent' halved is 'int'.
'int' put next to 'rude' is 'INTRUDE'.
(Other definitions for intrude that I've seen before include "Because of temperature, blue" , "Enter uninvited and unwelcome" , "Join in without being invited or wanted" , "Poke one's nose in" , "Encroach on others' privacy" .)