don't know about anybody else here, but i'll never let anyone ride my bike for more than a minute. for some reason, too, they all seem to want to skid my tires... why is that so cool to do? where is the fascination in it??? i mean, that tread is what keeps me safely stuck to the pavement/dirt!
One time, i felt like purposely ramming this one guy's rear wheel because he tried to do a one-eighty bunnyhop on my mtb(inconsiderate bmx rider). He didn't potato chip my wheel, but he put a hop in it... some people just don't understand.
my advice is, don't let anyone else ride your bike... they probably have no idea how dearly you love your bike... it may not be the best, butcha gotta love whatcha got.
... even the closest of friends should never, ever, EVER try to come between a man and his all-terrain-machine. it's just not a healthy idea.