Old-school D&D's penchant for magic items which appear to have some beneficial property and automatically defeat every conceivable test that would demonstrate otherwise, but the first time you use them in a life-or-death situation they can somehow tell that it's for real this time and suddenly reveal themselves to be horribly cursed has rightly been criticised as player-hostile bullshit, but the oft-unacknowledged corollary is that many of them are also, in context, extremely funny.
There's a flying broom that gets mad when you try to ride it and attempts to beat you to death with its handle. This is separate from, and unrelated to, the flying carpet that gets mad when you try to ride it and attempts to wrap you up and squeeze you to death.
There's a spear which performs normally in sparring matches, but in mortal combat it curves around to make you stab yourself in the back like some sort of fucking Looney Tunes gag.
There's a magic ring which appears to have the powers of a randomly chosen different magic ring, but in reality the only power it has is to employ mental illusions to trick its wearer into thinking it has powers. You are being gaslit by jewellery.
None of these require you to go to obscure sourcebooks, nor are they apparently particularly rare – they're just hanging out on the standard treasure tables in the Dungeon Master's Guide, ready to pop up in any random hoard.
You can even create them by accident by biffing your roll when crafting your own magic items (the roll in question of course being made secretly by the GM, so you can never know whether this has happened until it's too late), which implies several fascinating things about the nature of magic.
There's a hat that makes you stupid and it's plotting against you.
#That last one is definitely kink material (via @zoeyfromtheinternet)
The hat of stupidity isn't even the cursed item with the biggest kink potential on that particular page, let alone the whole book – the same section includes a belt that permanently changes your gender and a helmet that inverts your moral alignment.
(If we're willing to flip the page, we also get the horn of bubbles, which – as the name might suggest – surrounds the creature who blew the horn with masses of bubbles that follow them around and prevent all action for 2d10 minutes. I'm about 80% sure I've seen a kink meme with that exact premise on this site at some point.)
