Upset to see his ex-girlfriend with her new partner, Christopher James Rod took his emotions out on her car.
The pair had been separated for two months when Rod showed up where the victim and her partner were babysitting.
Police prosecutor Sergeant Drew Morrison told the Whanganui District Court that Rod became "angry" when he saw the new partner with his ex-girlfriend.
He went to the victim's car and kicked one of the doors before smashing a window. He went back to a ranchslider door and tried to open it, punching it on finding it locked.
Rod kicked the car again before leaving. When spoken to by police, he said he was sorry.