@subtext Something I’ve used in a handful of campaigns. is the “Deck of Many Answers”.

It appears as a deck of blank faced tarot sized cards. If discarded, the card vanishes and returns to the deck.

If a player asks a question before drawing a card, the card contains a hand drawn sketch attempting to illustrate the answer to the inquiry, but never with text or numbers. However, the deck is not omniscient and it’s answers getting increasingly symbolic and open to interpretation the more abstract or game breaking; the players inquire.

Usually found by players, with no instructions.

Figuring out the shtick usually provides a lot fun, and they end up being MILDLY useful should players get the hang of them.

Glasses of Magic Sight While looking through the glasses, a faint aura appears in the presence of magic within 30 feet, akin to the Detect Magic spell (no action required). You also have disadvantage on Perseption checks and Investigation checks while looking through the glasses as the magical aura of the Glasses of Magic Sight obscure your vision.

The vibrator of slicing.

This is a knife with two saw-like blades that move back and forth, allowing enhanced slicing of cooked or raw meats.

It gives advantage on all intimidate checks, with a +2 if wearing fishnets and/or high heels

One of my players really enjoys his Cloak of Billowing

An idol that periodically tells the current time of the day in a loud and clear voice. But only at night (or when the party likes to sneak).

I always try to have 2 Immovable Rods with my character so I basically have an infinite ladder. You can lock and unlock each rod and use them like rungs to climb things, cross gaps, etc. And they’re not really rare or expensive.

Maybe add the opposite of those; rods that never stop moving. Unstoppable Rods.

Ring of magic detection

As an action, you may use this ring to discover the location of the nearest magic item.

Something with a very niche useage like a Wand of Ring Detection; starts with 4 charges and regains 1d4 charges at dawn, expend a charge to become aware of any and all rings within 30ft.

Would usually be useless, until the one time you can use it to recover a lost/stolen ring or become aware of someone hiding their powerful magic item!
Or when they start using it at random and become aware of random little trivia of NPCs around them!

Also, chain mail would be obnoxious to someone using the wand!

A DM once gave me a necklace that could only be worn by neutral or worse alignments, and with a thought it would cause a torrential downpour of blood. The blood required a constitution check to prevent characters from puking. That was a pretty neat item.

Cook Pot of Concealment. Any edible item in the pot is invisible to a creature that could eat it until removed.

Earrings of No’Kyah: allows wearers to communicate by touching the earring while talking across any distance. Are also indestructible.

Boots of Courage: Provide +3 to initiative rolls, but have a 15% chance of tripping the wearer and leaving them probe each round they are retreating.

Bagawogs.

Squirrel sized, slimy creatures that infest pocket dimensions like bags of holding. They eat rations stored in them and occasionally weird you out by leaving a mucusey trail across your hand as you’re digging around.

Book of secrets. When opened, the book displays a secret whispered in the last minute, at least 50 miles away, somewhere on this plane.

Ring of invisibility. Doesn’t grant the wearer invisibility, it’s just invisible. If encountered in a shop the shopkeeper will be unable to find where they left it.

@subtext What degree and kind of silliness are you looking for? Merely not useful to adventurers, embarrassing in some way, implausible that they’d even exist…?