Skydiving
It doesn't take a genius to figure out that jumping out of a plane at 10,000 feet might be a little dangerous. However, as technology has progressed, skydiving injuries have gone down massively. The main causes of skydiving accidents continue to be DIY equipment, human error, and lack of preparedness.
You Know What You're Getting Yourself Into
Roughly 85% of skydiving injuries occur while landing (actually 100% of them do, but the causes aren't necessarily due to improper landings). Broken bones are the most common injury, but people regularly walk away with concussions, muscle tears, and sometimes not at all. There are roughly 25 skydiving deaths over the course of a typical year.