Progeria, because with Cretinism you'll have to live through the pain for a long, long time. Would you rather be lectured for 10 hours or attempt to hide under the train when it's passing with a 99% chance of dying after jumping from a station platform?
The wall tries to play soccer. But then he gets intestinal bleeding, which is later found to be necrotizing fasciitis which eats up all of his skin around his guts. 55 HP.
Violent stomach cramps. Would you rather get necrotizing fasciitis from your groin up to your chest or get a severe allergic reaction whenever you're near concrete? http://en.wikipedia.org/wiki/Necrotizing_fasciitis <-- That's what necrotizing fasciitis is.
Where the hell did you get that from? Dumpster. Would you rather be that guy who gets an axe in his head in The Shining or would you rather have someone slowly and painfully kill you with a dagger?
When someone gets 200m XP in all skills the entire game will implode and everyone will start as a level 3 noob with a bronze hatchet, a tinderbox, and some food.