I can honestly say that I've never gotten nailed from behind, skier or snowboarder.
My undignified injury did happen to my ass, though. Freshman year spring break I went to Whistler with my friend and his dad. His dad's friend bet that nobody would drink a whole bottle of Habanero hot sauce called "Fear Itself" for $20. Well, $20 would've paid for a few poor college student's meals, or half a lift ticket so I was game. I had to drink it over the course of the meal, but I figured I should get it over with early. I didn't eat my dinner, as it felt like my intestines were slowly dissolving. I was also up all night pooping lava. Not fun.