I'd be curious to see a trap that "attaches itself" to a PC with unused attunement slots when touched or examined closely. Makes the slot temporarily unusable and it triggers some sort of trap effect (elemental damage, instant pit trap, instant falling block, unwanted teleportation, baleful polymorph, etc.) when you attempt to unattune or divest yourself of the item (I'm visualizing it as a sort of ioun stone that floats about the target). The more powerful ones not only take up a slot, but do something detrimental as well (from magic mouth to conditions such as poisoned, restrained, or even damage over time - a nasty one might paralyze). Remove curse would probably be the primary way to deactivating it without triggering it.
It could be insidious with items that offer extra attunement slots with this sort of trap in mind, especially if those extra attunement slots are keyed to favor being filled/overidden by the above traps.