You crash your friend's car because you're driving too fast in bad weather. Everyone's okay, but the car has to go into the shop. Who pays the deductible?
What a retarded question. When does the "Your friend has pissed you off beyond belief, fucked your bf/gf, and broke your favorite mug.... How many times do you stab them?" QotD come up? Let me know, I'll take the day off.
Seriously. I'm a pretty careful driver and if I borrowed someones car, I intend it will be driven back to them intact with whatever gas I used replaced. If by some circumstance, I did some damage to their car and I was at fault, I'd pay the deductible. I probably would either way, I'm a pretty decent guy. Thing is, I have my own car and even when people offer me theirs when they're parked in back of my, I insist on using my own. Then I don't have to worry about it.