absurd, asinine, balmy, barmy [chiefly British], batty, brainless, bubbleheaded, cockeyed, crackbrained, crackpot, crazy, daffy, daft, dippy, dotty, fatuous, featherheaded, fool, foolish, fruity [slang], gaga, half-baked, half-witted, harebrained, inept, insane, jerky, kooky (also kookie), loony (also looney), loony tunes (or looney ​tunes), lunatic [informal], lunkheaded, mad, meshuga (or meshugge also meshugah or meshuggah), nonsensical, nutty, preposterous, sappy, screwball,