Something we used to do at recess in Oklahoma was play 'chicken' with boot knives. The two challengers would stand a few feet part, facing each other, and one would throw his knife so that it stuck in the ground between the boots of the other, and then step back a step. The other would throw, then step back a step, etc. until one of them chickened out, usually when they were standing several yards apart (and both would be standing with feet pretty darn far apart!).
Playing catch with knives (or razor-tip arrowheads, on hunting trips, while drinking Coors) was also popular.
'Racking' (two parties kicking each other in the nuts as hard as they could, until one party gave up) was another one that was more fun to watch than play. [Although, when you nail someone hard enough that both of their feet leave the ground? You get picked on less...]
I've heard of, but never seen, 'Irish boxing' where two guys take turns punching each other in the head as hard as they can until one quits (or is knocked out).
Arm-wrestling over live scorpions is from some movie, but I'm sure some nutjobs somewhere have actually done it.
More medieval 'fun and games' could involve holding a hot coal from the hearth for longer than the other guy, or stripping shirtless and taking shots at each other with whips or slender branches until someone gives up would also fit the theme of 'crazy things people do on a dare.'
Some sort of sumo like wrestling game where the circle was surrounded with caltrops, so that anyone who stepped (or fell) out of the ring got many tiny ouchies, would also fit a barbaric theme.
Russian roulette with a crossbow could be amusing. Since a crossbow doesn't have a revolver, it could use a Repeating Crossbow with 1 sharp bolt and 7 padded ones that just sting slightly, and the dude you are playing the game with gets to fire the crossbow at your chest (and hope you get the sharp bolt and he gets the padded ones!).