Grapes

Eaten straight they give a middling food buff. Two of them turned into Grape Juice push you up a tier of the same buff for the same drop, so there is little reason to eat them raw once you know the recipe.

They sit outside the fruit group entirely, so they will not go into Fruit Salad, Ambrosia or Fruit Juice, and no amount of shaking trees produces one. They come off Derplings and Giant Flying Foxes in the Hardmode Jungle instead, which means you collect them while farming something else and rarely go looking on purpose.

The tooltip nods at The Grapes of Wrath, and the flying fox drop is a second joke on top: the fox in the old fable decides the grapes were sour once it cannot reach them.