Not the most dramatic cursed item, but definitely one of the most frustrating...
Stone of Distraction
A stone of distraction seems to be a stone of concentration at first, encouraging one to focus one's thoughts at the task at hand the moment it is touched or seen, but soon enough it becomes apparent that instead of freeing one from distractions, it amplifies them. Every sound becomes louder and more jarring. The slightest physical contact is either ticklish or itchy. Light is too glaring. Shadows are too mysterious. Colors are too colorful. Anything and everything becomes a consideration except whatever it is one wants to do. Exposure to a stone of distraction utterly precludes the casting or memorization of spells, of course, and even light reading is impossible under its influence. The curse will operate whether the stone is seen, touched, or on one's person, and only the spell remove curse will rid one of it.
Like other magic stones, a stone of distraction has no standard size, shape, or coloration.