I can think of many things I wouldn't even do once because I know I would hate them: scuba diving (claustrophobic plus I could drown), caving/potholing (claustrophobic, plus I could get stuck and die a slow horrible death) (plus I hate the dark), white water rafting (I could die), bungee jumping (i could die plus I could get a detached retina), parachuting (I could die, or just get horribly injured).
I have been skiing several times and loved it, but wouldn't now because of the risk of injury. Ditto parasailing.
I have now thought of the thing I've done once, never to be repeated. Think I had blanked it out tbh...
Went out on the St Lawrence River in a small speedboat with my DP, who was experienced in boats, he said he would do everything and we would stay close to the banks, so I reluctantly agreed.
For info, the St Lawrence is very deep, hence is a major shipping route for MASSIVE ships. For further context, the previous evening we watched from our riverside restaurant horrified as a body was pulled out of the water AFTER A BOATING ACCIDENT. Another diner helpfully explained that the water was so cold you die of hypothermia before you drown. Okay then 😳
Anyway, back to the rental... after we'd paid for the hire the renter explained that the one not 'driving' the boat would have to navigate , and we had to quickly get out into the main body of the river as there were dangerous rocks underwater along the sides of the river.
Handed me the navigation maps - cue panic on my part.
DP says it will be fine. Off we set, guns the boat a little to cross another boat's wake, its safer apparently, but water washes over the boat and us as we head out into the middle of the river. Cue screaming and swearing from me, swearing from DP.
We found somewhere to dock as soon as we could. Went in search of a cafe, didn't find one, returned to the as it turned out private dock to find the owners tying up their boats. They were friendly once we explained the situation. They invited us back to theirs for lunch, drinks and many laughs.
Then we got back into our boat, and returned it. Covered almost zero miles. Huge waste of money.
Never ever again doing the smal boat/huge river thing.