Sky diving is the one that immediately comes to mind for me too, but maybe for a different reason than some. I'm okay with the jumping out part, but I HATE to fly. I'll only do it when it is a necessary evil - when I don't have enough time to drive to the destination I want to see or if it can't be driven to (ie, other continents). I especially hate small planes. I won't get on anything smaller than a 737 any more, after a couple of terrifyingly rough flights on 717s between Detroit and Orlando, so there's no way I'm going up in the kind of planes skydivers jump out of!
I don't have any interest in climbing mountains if that climb goes beyond a challenging hike. I'd climb Fujisan if I'm ever in Japan during the season, but I'm not interested in Everest or Half Dome.
Other than that, I'm open to most things. My personal bucket list is mostly travel experiences - seeing all 50 states and a long list of countries, sites and wonders of the world.