Following up on discussions elsewhere about the Titan sub - and risk evaluation, understanding the risks and the safety precautions in the activity to ensure that the risks were mitigated.
I've done scuba diving in deep ship wrecks - actually going into a wreck. Looking back, it was probably quite risky - it was deep and I am not sure that the nearest decompression chamber was that close. But I was young and it was one hell of an experience.
But I wouldn't do bunjee jumping. I would worry about my eyes and retina.
Someone on another thread mentioned going in a hot air balloon. I would do that but they wouldn't. I guess that if those go wrong, there is a chance of plunging to death.
So what would to do / not do that others might consider risky or others would consider absolutely fine.