I've been in a few situations where I've let people use my car.
1. EF Hatch. Stock mostly. Let my brother use it for work. Blew it up.
2. 71 Nova (before mods) Straight 6. Let my uncle use it. Ditched it on a SUMMER day said he hit a wet spot (he was drunk) *asshole*
3. EK Coupe Intake exhaust only. Got pulled over one night, had an outstanding ticket warrant for bad inspection (pa). Spent the night in jail. Was on the way home from picking up my cousin and her son with her brother. He didnt have a liscense. Got pulled over for a head light out. She drove off and missed 3 gears in one shift

Once they turned the corner her brother drove it.
4. Same car, same guy. Needed to run an errand, the very next morning while i was in court for that ticket lol. Made it 2 blocks from his house, the cam locked up in the head(oil was full and new) snapped the timing belt.
One thing i love more than my cars is my dirtbike. I let a friend of mine race my KTM 125 a few times. One time he lost it on a sweeper, and drilled a light pole at a night race. Twisted the front end, smashed my pipe, bent the bars, broke both clutch and brake lever. Luckily i was done with my classes for the night. The next day I called him asking to help me with just straightening it out, and maybe clean my air filters for me. I didnt think that was much to ask. I didnt even ask fro money to fix things. He told me he had no ride. I went and got him, all he did was sit on his ass and watch me do all the work. I'll probably never let people use my equipment again, unless i have something of theirs for collateral
Gotta love friends