Captured on security footage, the moment Watson the black sheep attacks the newly repaired Toyota of his owner, Shiree Palmer.

Shiree Palmer's stationwagon had just come back from the panel beaters, gleaming and fully repaired after a crash.

So she was none too pleased to go out the next morning to find someone had already dented the passenger-side door as the Toyota was parked in the gated front yard of her lifestyle block in Otaki.

The vet nurse was admiring the work on the driver's side when partner Hamish Fleming asked: "What the hell happened to the other side?"

ROSS GIBLIN/ FAIRFAX NZ Shiree Palmer and Watson survey the damage to her Toyota stationwagon, which had just come back from the panel beaters when Watson attacked his reflection in the door.

"I said, 'what do you mean?'. He said 'well, it's really dented'."

"I hadn't even used the bloody thing since I got it back," she said.

The yard is monitored by a security camera, which the couple immediately checked. "That's when we saw Watson at work."

The vandal turned out to be their pet black sheep, who had repeatedly given the door a good working over with his head – possibly because the paintwork was so clean that he was startled by his reflection.

"The car was so clean and it's usually dirty," Palmer said. "I think he thought it was another sheep and it was a threat, and that's why he did it so many times."

The camera footage clearly shows Watson – a desexed one-year-old named after Paul Watson, captain of hardcore environmentalist ship Sea Shepherd – facing off against the rear passenger door of the Toyota, watched rather nervously by a pair of alpacas.

Watson slams the door with his head, again and again. Perhaps sensing things are getting out of hand, the alpacas walk away.

A white sheep called Boots stands in the shade below a nearby tree, watching.

"I was absolutely gutted, because it happened about 15 minutes after I opened the gate to let them in the front yard," Palmer said. "My heart sank."

Palmer will not be able to afford to get the battered door replaced immediately. If she claimed insurance she would have to pay the excess and face losing a big chunk of her no-claims bonus, so it was not worth it, she said.

Despite his attack, Watson's only punishment was a spot of social media shaming.

"Hamish is calling him pot-roast, but that won't happen," Palmer said.