Mine would be free climbing(without any gear whatsoever) since I was ~14 years old. I've been close to a fatal fall at least 3 times, and the guy I climbed with was going to get seriously injured(at the least) if I hadn't caught him. However, spring is coming, and I plan to resume climbing as soon as possible. I dislike the winter for this reason - climbing without gear + ice = inevitable fail.

There was also that one time as a kid where we were in a remote village visiting a friend's family, and it had been snowing for a while. There was at least half a meter of snow on the ground. Then, I had the genius idea to go sledding alone(since everyone else said that it was cold as f*ck, but hey, I wanted to go sledding), while promising that I wouldn't go too far. Then of course I did what everyone would have done, and went too far. Somehow it didn't register with me that going down steep hills is easy(especially with a sled), but going up is much more problematic. So, in summary:

Happy sledding time = 30 minutes.
Getting back to the village while going around or through the huge steep ice&snow covered hills = at least 3 hours.

Of course cell phones were nearly non-existent at that time, and I had told them not to expect me anytime soon. The last steep hill in particular probably took me at least an hour, I must have fallen down at least 40 times and I was extremely exhausted when I finally managed to get back.

Those are my "gotten in serious trouble" moments, everything else can't compare to death or serious injuries