Some type of melon, I imagine. A distribution of NetHack I installed once had this set as the default fruit name, leading to "My, that was a yummy yiffmelon" as well as tasty potions of yiffmelon juice. At least yiffmelon is something I could probably stomach, unlike slime mold, the usual default.

My, that was a yummy slime mold
the fungus that grows on dungeon floors cold.
but yiffmelon be yet easier to swallow,
ere Arch-Lich comes and Demogorgon follows.