Force out extra impolite (7)

I believe the answer is:

extrude

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'force out' is the definition.
(I've seen this before)

'extra impolite' is the wordplay.
'extra' becomes 'ex' (I've seen this in other clues).
'impolite' becomes 'trude' (I can't explain this - if you can you should give a lot more credence to this answer).
'ex'+'trude'='EXTRUDE'

Can you help me to learn more?

(Other definitions for extrude that I've seen before include "Force out (through die)" , "Thrust or force out" , "feature obviously?" , "Eject" , "Squeeze out" .)

I've seen this clue in the Sydney Morning Herald.

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