Try the salt and ice challenge, pour some salt on the palm of your hand and squeeze an ice cube, salt instantly freezes and will burn your skin, it leaves a permanent scar and stings pretty bad but not enough to shed a few tears, also there is the banana and sprite challenge, eat 2 banana's and drink a cup of sprite and try not to throw up, it doesn't make you throw up when i tried it, it just gives you pain on the side of your stomach. There is also the raw egg challenge, you eat a raw egg, there is the lemon burn challenge, you cut yourself with a razor blade and squeeze lemon juice over it ( don't do it only idiots do that one) and the last one is the orange peel challenge, you have to eat the peel of an orange which is very bitter and gross. Have Fun!
Some of the hard challenges are the Bread Challenge, where you are expected to eat a whole piece of bread in 45 seconds, and then there is the Saltine Challenge, where six saltine crackers are eaten in 60 seconds. There is also the Banana and Sprite Challenge, as well as the Milk Challenge. More examples can be found at http://topher2.hubpages.com/hub/The-Top-5-Internet-Challenges.