Parkour is a discipline, not throwing yourself into some flip you've never practiced. Risk is always a factor, but managing risks is a bigger part for anyone who practices parkour.
Just don't. If someone dares you to do something you aren't 100% confident in, you shouldn't try it. People who practice parkour correctly realize the risk and encourage people to expand their limits, but don't dare people to things they will probably fail.
When you jump off a small ledge, curb, or anything that small, and call it parkour you just look dumb. If you're making fun of people that are practicing but aren't good, you should stop because they'll probably be able to show you up pretty soon.
Yes this is stupid, but I actually met a kid that thought I was talking about minecraft when I said I do parkour. My response... *facepalm*
Watch all the parkour videos you want and anyone doing anything legit never yells parkour while their doing it. If you do you look stupid.
select one here...