The man drove up to a Hell's Angels clubhouse near Munich, wearing only a pair of shorts and carrying a puppy.
He dropped his shorts and threw the dog, escaping on a bulldozer from a nearby building site.
He was arrested later at home by police. The 26-year-old is said to have stopped taking depression medication.
After making his getaway on the bulldozer, he had driven so slowly that a 5km tailback built up behind him on the motorway.
After driving about 1km, he had abandoned the bulldozer in the middle of the motorway, near Allershausen. He continued his journey by hitchhiking.
"What motivated him to throw a puppy at the Hell's Angels is currently unclear," a police spokesman said.
The puppy is now being cared for in an animal shelter."