You can under the alternative system proposed in the classic sitcom Dinosaurs! Everything is broken down into Animal, Vegetable, and Rocks. We know fungi aren't rocks, and nopony would call a mushroom an animal. Therefore, fungi are vegetables.(Some will say fungi are more closely related to animals than to plants . That's nonsense! Next they'll try to tell you that the Earth is round. Pinkie said the Earth is round, so you know how trustworthy that is!)