My last bike was a Kawasaki Vulcan 800 cruiser that I bought for $600 in non-running condition (carb).
The bike was rusty and such, so I didn't think I really cared who rode it. But in retrospect, the numerous co-workers that I let ride it were chosen by me - not by them.
In other words, now that I think about it I'm sure there are a ton of people who could have asked me and I would have denied. Yet in one year's time I let about 6 people ride the bike, and had open invitations to many more.
Back in the day when I had a pristine ZX-7R I did have a very, very good friend ask (actually, he was pretty pushy) to ride it, but I knew his riding skills, and knew he had no experience with horsepower nor the quirky handling of a sport bike. It took a lot to say 'No. Sorry Mike" (multiple times), but looking back I'm sure I made the right decision.
"After reading through this thread I've come to the conclusion that more people cruise the internet looking for reasons why X bike won't work in Y scenario rather than actually riding their motorcycles." -- RyanR