Driving south in State Highway 1 near Henley, Macnee passed a car on a blind corner, causing an oncoming vehicle to take evasive action.
It was just the start of a perilous episode.
Entering Waihola, the defendant then weaved wildly across both lanes of the highway.
"That section of road is extremely well known," Crosbie said. "There are all sorts of bends."
A vehicle ahead of Macnee noticed his erratic steering and used his horn along with hand gestures to alert oncoming traffic to the unfolding drama.
As the defendant approached him from behind, the driver dabbed his brakes in a bid to slow him down.
Instead, Macnee passed on the left, mounting the footpath to get around the vehicle.
"Trying to take someone on the inside?" the judge said.
"That is appalling and very scary driving."
And it continued.
On the way into Milton, Macnee caught up to a vehicle towing a trailer.
As he swerved round it, he clipped the trailer before finally pulling over.
"His speech was slow, he was stuttering, his eyes were glazed and he was unsteady on his feet," police said.
But before they could assess his faculties they had to get him out of the car.
Macnee was so incapacitated a member of the public had to take off his seat belt and assist him to his feet, the court heard.
A blood test revealed the smorgasbord of substances the defendant had combined.
"This driving is as bad as it gets," Crosbie said.
"It's luck and nothing else that saw no-one was injured, or worse."
Stephenson said community detention was the appropriate sentence and would allow Macnee to look after his sick mother.
The judge disagreed.
Macnee was jailed for eight months, ordered to pay $750 reparation and banned from driving for two years.
