I think we need to note a few things. I've already said that I would warn the player if their actions would bring about their death. Omitting that from your example makes me look like a callous jerk and I think that's unfair. Another important thing to note is that the player has a good narrative reason for wanting to jump. He didn't just decide to jump because he didn't want to take the time to walk or something silly like that.
There are people in real life who risk injury doing stupid things.
My Dad to me when I was a boy: "If you fall off that wall and break both your legs, don't come running to me!"
People also do stupid stuff in games. I actually hate that kind of behaviour, in real life or in game. I would hate it if a player had his PC jump off a cliff for nothing but the lulz,
but I wouldn't change the rules just to vex him!
Just like a real life person taking unnecessary risks just for fun, the player knows that the fall will cost him about 70 hit points. Having 200 hit points doesn't make the instant loss of 70 of them meaningless. If the player does this, it may come to haunt him if he's in a fight before the next long rest. No, I wouldn't have the universe spontaneously generate a 'grudge' of tarrasques (my new collective noun for tarrasques), just realistic consequences. It may bite him in the butt (his foolishness, not the tarrasques), it may not.
BTW, I'm confident that trolls
know they can regenerate (and know that fire stops it), and wouldn't be surprised if some evolved a culture of doing stupid stuff to show off how hard they are to their mates. I wouldn't be surprised if a rowdy set of trolls jumped off the cliff just to get to the other side, laughing as they went, then show off their muscles for a few rounds pre-combat (for the intimidation factor AND the regenerated hit points). In fact, that's such a great scene I can't wait to use it myself!
TLDR: neither acting rationally nor acting foolishly should cause the DM to essentially cheat by altering the laws of the universe to punish. Let the game roll on, and naturally wise decisions will out-evolve foolish ones.
Let the dice fall where they may. Don't metaphorically change the dice to punish behaviour
you don't like, especially on a subject where mileage varies so much.