The 26-year-old drove onto the biker clubhouse grounds on Sunday afternoon in Allershausen, a town just north of Munich, daily tz reported on Monday.
There the Munich student pulled down his Bermuda shorts, mooning a group of bikers before throwing a puppy at them, the paper said.
Then the man fled the scene, stopping at an autobahn construction site to steal a front loader, which he attempted to drive to Munich.
But his slow pace caused a 5-kilometre traffic jam, the paper reported.
After making it just one kilometre along the highway, the 26-year-old hitched a ride with a truck, which let him off in Eching, not far from Munich.
Police lost track of him for a while there, but they quickly located him again, finding out that he had neglected to take his medication for depression.
He was checked into a psychiatric clinic for treatment. Meanwhile the puppy he tossed at the bikers is being cared for by a Freising animal shelter.