1. Volcano boarding
Before you ask, no, they are nut surfing in the lava, but what they are doing is extremely stupid anyways. Apparently the best place to do this is in Nicaragua, at a volcano of about 725 meters high. Since the board they are using can get up to a speed of 80 km/h, it's no surprise that they are in need of special protection...
2. Wing Walking
This isn't actually a sport, more like a stunt. But it's still highly irresponsible to do it, since you are usually traveling with about 200 km/h. I'm still trying to imagine how anyone can breath at that speed, since I even have troubles with it when a bigger wind blows.
3. Train surfing
I think I probably know how this "sport" came alive. Must have been the train of death in India, where so many people get on a train that there are some literally hanging from the top of it. I don't really know how this can be allowed, since the people doing it are highly unprotected, and there are too many things that could go wrong with this.
4. Slacklining
Ok, so you are familiar with the guys who perform this in a circus or other. I'm not exactly sure if this is an extreme sport or not, since if you can walk on a rope like that above ground only a few meters you should be able to do it even if it's as high as a few kilometers. The problem, I think, might come when you look down...
5. Base jumping
So, most base jumpers use only parachutes for their stunts. They jump down not only from cliffs, but from high buildings too, so if you see one in your city don't be alarmed. The more extreme version of this is with the wingsuit. This suit, as I think about it, must turn you into a human kite, or something. It will help you stay in the sky for a bit longer. If I were to try out an extreme sport in my life, this would probably be it.
