Parasailing while on holiday - towed behind a boat in a harness with a parachute thingy so that you are shot into the air God knows how many feet up at the speed of light, or that's what it felt like. And I was constantly petrified at the thought of the rope breaking! And I knew all along that I was going to hate it - and it wasn't exactly cheap, either.
I was talked (or badgered) into it by dds, who loved it and thought I was such a wimp not to have a go. Well, I AM a wimp, and since then I have never let myself be talked into anything if I know I'm going to hate it, just to show my lack of wimp-ness.
Some years later elder dd (who hasn't inherited my wispiness) confessed that although she was petrified at the time and wanted to wimp out but couldn't bring herself to admit she was scared, she HATED her bungee-jump in New Zealand and said, 'Don't ever do it, Mum - you'd hate it.'
As if I needed telling!