A fruitloop is someone other people call crazy, or whose ideas sound wild. It is slang — playful American talk, sometimes unkind. You might hear it about a neighbour with strange theories, not in a doctor's room. Though actually, it is not a careful word for real illness; it is a joke-insult, and it can sting. It is also written as two words, fruit loop. The name probably mixes fruity and loopy (both can mean 'a bit mad'), and the bright breakfast cereal Froot Loops may have helped the sound stick.

瘋子；怪人（口語，帶玩笑或輕蔑）