Easy. Bunch of friends and I did magic mushrooms. One "friend" {read: aquaintance} disappeared... later, he drove by. Fucking idiot. Maybe a year after that, he totalled his 2nd or 3rd car by driving home drunk and going like 150kph in a 70, sliding out on a turn, and rolling his car about 6 times.
For myself, easily the closest call I had was in my first car, a 1980 Datsun 280ZX. I was on a 2 lane (1 in each direction) highway. Came up on a big truck that was going slow and we had the "passing allowed" centerline. No traffic in sight. I "booted it" (this car wasn't exactly fast) but I think the truck sped up too... Suddenly as I'm basically beside the driver of the big semi, some cars appear over the hill ahead. I just barely managed to get in front of the semi and a huge Dodge Ram flew by going the other way. It was terrifyingly close and to this day I don't know if that semi driver was being an ass (speeding up) or if I was just being totally stupid. Regardless, I've been a lot more careful in those situations ever since.