Affected with madness; insane. Informal Departing from proportion or moderation, especially: Informal Possessed by enthusiasm or excitement: The crowd at the game went crazy. Informal Immoderately fond; infatuated: was crazy about boys. Informal Intensely involved or preoccupied: is crazy about cars and racing. Informal Foolish or impractical; senseless: a crazy scheme for making quick money. One who is or appears insane: "To them she is not a brusque crazy, but 'appropriately passionate'\u201d ( Mary McGrory). like crazy Informal To an exceeding degree: They were running around like crazy.