The eggplant is possibly the most obviously poorly named fruit or vegetable, neck-and-neck with the pineapple. Its name came from the fact that some cultivars used to be white, and better resembled eggs than the purple variety today. However, before they were called eggplants, they had another name in English: mad apples. It was believed that eating the eggplant would cause insanity, and so they acquired the names of mad apples and rage apples.
(As for the pineapple, it comes from the fact that pine cones used to be called pine apples. Pineapples resembled pine cones, and the name was used for them, and persisted long after it stopped being used for the pine cones themselves, hence why pineapples have no connections to pines nor apples.)