My tolerance is at a bit of a meta level. I can stomach most dark themes presented in stories. If there's one theme I can't stomach, I have yet heard of it.
What I CAN'T stomach however, is edginess. Not the fun kind of edgy where a black-haired Dante fucks 5 chicks with the edge of his pistol bayonet but the ones that are badly written. I'm the guy that ruins parties. I can't stand it if the characters don't make sense or do dark shit just because, or that dark shit happens because it's dark shit.
And no, "bruh he's a human he's prone to making bad decisions" isn't a viable reason. It's plain autism stupid when a bad guy does bad thing just because it's evil (that Russian general from the MW reboot) and worse if the story itself tries to paint them as sympathetic and, hell, even good (the main cast of TLOU II, yes I'm still salty about it).