Hmm...well, it wasn't on a bike. But it only had one wheel, so that makes it better than a bike, right?
I was 18 and out in Driggs, Idaho flying sailplanes. I'd soloed the day before and I had done at least ten hops that day. I was feeling pretty confident. And in an 18 year old male, that's a bad thing. It always leads to trouble.
I was flying one of the airport's two Blanik L-13's. They look like this.
http://www.cumulus-soaring.com/soarmn/photos/L13_640.jpg
I was coming in for a landing from the northeast. There were storms approaching, so I'd already decided it was time to get on the ground and tie down the aircraft.
Here's a section of the runway. The second L-13 was already tied down in the gravel where the taxiway and the runway meet.
driggs, idaho - Google Maps
I touched down and was rolling along happily on the sailplane's single wheel (very fun, it's like flying on the ground.) and thought,"I really don't want to push this beast to the tiedowns. I bet I've got enough speed to make it."
Well, I did. I coasted up on the left side of the other L-13, which was tied with its left wing up and right wing down. As I came to a stop I used the ailerons to bank my aircraft and at the same time used the brakes. I came to a stop perfectly positioned. My right wing came down and I was stopped. Perfection itself!
The ground crew came out and the owner of the sailplanes was with them. He looked at the aircraft, and looked at me and asked,"How did you get the airplane there?"
"I stopped short of the tiedowns and then pushed it in while you were coming out in the truck." I replied.
Anyway, as to why this was stupid...
Airplane parts aren't cheap. I could have easily gotten too close and failed to drop the right wing. All it would have taken was a gust of wind from my right side. Had that wing gone up, I would have done major damage to two sailplanes. And a lot of those parts can't be had anymore, or must be custom made.
As for the most dangerous thing I've done on a motorcycle, I'd say trying to wheelie a K75. Every rotating part in that bike's drivetrain runs lengthwise. Front wheel goes up, and the torque sends the whole bike sideways. Not good at all, and I almost wrecked it.