having the water pump let go out in the middle of nowhere. that was an expensive tow home. and the convertable with the roof down behind me that got covered in white smoke wasn't too happy. sorry!
having the local bmw dealer somehow manage to snap my gear lever while it was in for a service then try to charge me to fix it. never been back there again.
i've had one spin out in the rain, but thats because i deliberately kicked the back end out around a corner and tried to go a little more sideways.... ended parked nicely against the kerb on the other side of the road. didn't touch the kerb, looked like someone had done a really good parking job

but that wasn't a bad experience, that was just a bit of a loose at low speed. was very funny when it happened because it all happened so slow but i still had no chance in hell of catching it. just laughed my arse off when i realised where and how the car had stopped.