I don't read superhero comics (for the sake of my own mental health), but i need to dump some of the batshit insane things i've heard second-handedly over the years:
Symbiots aren't weak to fire because of some, like, physical reason. It just really triggers them.
Superman has used his laser vision to give someone a lobotomy at least once.
Batman has watched Sailor Moon.
Tony Stark gave Daredevil his sight back, only to take it away again immediately, just to be a dick.
The only reason Doctor Doom is still evil is because the Human Torch fucked his wife.
The Hulk is the reincarnation of the Devil
Apparently, Watchmen just. Coexists with the other DC stuff. Which is ludicrous.
Venom gaslit Eddie into thinking he had cancer. This ended up making Eddie more powerful.
Like half of Gotham knows Batman's identity because they checked Robin's adoption papers.
The Flash is faster than light, but one of his recurring villains is a normal guy, with normal reaction times, who has a freeze ray.
Writers keep repurposing those weird, goofy silver-age villains. And either make them complete jokes and beat the shit out of them, or make them fucking terrifying.
Supaidah-Man (i.e. that japanese tokusatsu Spider-Man show) wasn't a bootleg and is actually a canon alternate universe.
Batman canonically pissed himself during that one speech in Year One.
There are a bunch of shit-tier X-men with useless powers. Like the guy with invisible skin. Or the kid who can explode once and immediately die.
The Reverse Flash once travelled back in time just to kick kid Barry down a flight of stairs.
Cyclops' power isn't laser vision. Rather, his eyes are simply portals to the Punch Dimension.
The Joker became the ambassador of Iran in order to gain diplomatic immunity.
Green Lanterns are weak to the colour yellow (this one might have been a joke?).
There's pink kryptonite that turns you gay (this one HAS to be a joke).