I only let someone else ride my bike once...and it turned out as expected.
I had a DRZ400S at the time, and we were having a get together at my cabin for the weekend, and my bike happened to be there.
One of my buddies asked if he could take it for a spin.....I hesitated a bit, but he promised he could "handle it".
The road by the cabin goes in a circle about the size of a city block (but the road is just dirt, and hemmed by tress along both sides). I am down by the lake, and I can hear my bike roaring around the circle (now, you know a DRZ is being hammered on when you can hear it "roaring" with the stock exhaust.
Suddenly, all goes quiet.....
A few minutes later, my buddy comes back on the bike and both he and the bike are totally covered in black mud and cattails. He goosed it a bit too hard in one of the corners, and went off the road right into the only bit of swamp along the road (thankfully, he did not go off anywhere else, as it is all cedar trees). He had gone head first over the bars and really "stuck" the landing right in a big patch of cattails.
Thankfully, the bike was unharmed and did not suck any water into the engine.
He actually went out into the lake fully clothed (including helmet) to wash the first couple of layers of mud off.