Quote: Surely it depends on the level of trust and relationship.
I am not that touchy about my bikes. I trust my friends. That is why they are my friends.
I do understand the mentality of "Nobody rides my bike". They are extensions of our personalities and we prefer they not be wrecked. With a few folks I don't subscribe to it.
Now other folks I don't know throwing a leg over, that is another story all together.
This is basically the way I am. I actually bought a relatively inexpensive second bike from Craigslist(used 2001 Triumph Thunderbird) for friends and relatives to ride when they are in town...and, sometimes I let them ride my Speedy, and I ride the triple (which I have grown quite fond of)...
With that said, I would never throw a leg over someone else's bike without prior permission...