Another male at the party later discovered the man fondling the by-then unconscious woman's exposed breasts and watching his son engage in sexual activity with the woman.
The witness and another person put the woman's clothes on and moved her to a bedroom.
But the man then refused to give them their car keys and kicked them out of the house, physically blocking them from re-entering, according to police.
The witness eventually got back into the house and discovered the man's semi-naked son on top of the still-unconscious woman, whose underwear had been removed.
At a hearing in October, Judge Sharp said there was no suggestion the man had drugged the woman but it was "alarming and sinister that the suggestion was ever made".
The man was a "bad father", one that his son could "probably do without learning any more from", she said.
She encouraged him to "take a long hard look at himself", especially around his alcohol consumption, for which he was ordered to receive treatment on as part of his sentence.
cherie.howie@hos.co.nz