The only one I can think of is a fear of heights. I've never bungee jumped, nor parachuted ...and I doubt I ever will. I don't mind airplanes or roller coasters, however -- I guess it helps to have the one level of safety represented by a seat belt or a window.

While I don't come completely unglued if I'm near a cliff's edge, my legs get rubbery and my scalp prickles. (As Hobbes the tiger would put it, my tail gets all bushy). I can function with it -- or I wouldn't have done any mountain hiking with my Scout troop. But heights are the only sure-fire way I know to turn my insides to water.