Headband of miner intellect:

• Forged by a dwarven artificer who lost too many colleagues due to their lax attitude around safety.

• Anyone wearing this headband becomes aware of the quality of air and props for whatever tunnel they're currently in.

• Wearers possess an intrusive urge to find proper protective equipment before attempting a task.

Caltrops of Seeking. Drawn to metal and increase chance to damage/hit metal boots.

They stick together though and must be manually placed one by one over an extended period of time.

Sword of ghostly might: One owned by a powerful warrior who came back as a vengeful spirit. Neglects to mention that the sword is also a ghost, and therefore can only deal damage to spirits.

The "Sword of Instant Regret". It does 100% DMG, but only stabs the wielder.

"Wizards with Guns" did a couple of sketches based on this concept.

Cloak of Levitation, but it just lets you float a foot off the ground without moving.

Hulk Strength, but dumber than Hulk. You smash anything in the area, including your supplies/allies/horse...

Cap of Invisibility, but you can't see anything either.

Wand of Premature Eruption: Launches a fireball that detonates immediately

A magic sword that can instantly kill anything it touches but it's stuck in it sheath and can't be removed.

Magic rope - an animated rope that can be commanded to levitate and tie knots. When placed in any container, pouch or pocket, it immediately gets tangled up and take 1d6 minutes per 5ft of rope to untangle. Other objects in the container also become tangled with the rope, and take 1d6 minutes to remove individually, entangled objects are released immediately when the entire rope is untangled.

Magic rope is unable to be cut by any non-magical item.

Immovable Rod:

• Not actually a magical rod.

• Actually just a bloke called Roderick, or Rodney, or something to that effect.

• Won't move out of your way.

• Not even if you ask politely.

I feel like this would fit here nicely

Sword of Bludgeoning

+5 impact damage -2 stab damage

Only 10% off, because pommel strikes are op

Flail of Flatulence: deals an additional 1d4 of embarrassment to the target while dealing 1d4 of gas damage to everything within 6 meters.

Invisibility potion that turns your digestive track and stomach contents invisible.

Lembas bread but it's 1000 years past it's due date and you will get diarrhoea equivalent to its food value.

Scroll of Gorilla Warfare. When used summons 15 gorillas. These gorillas are wild and do not obey orders given by the caster.

Skull of Corruption: It can do damage, but most of the time to your invaluable backup files.