sappy, zestful, harebrained, asinine, witless, cuckoo, haywire, cranky, stupid, nonsensical, zesty, chapped, maniac, awry, fatuous, loony, not in your right mind/not right in the head, daffy, lunkheaded, mental, absurd, amiss, crackers, crazy as a loon, silly, dotty, psychotic, distraught, barmy, scatty, half-witted, disordered, crazed, wacko, crackpot, bonkers, wacky, foolish, jerky, crazy, not all there, sane, kooky, unbalanced, balmy, insane, wild, over-the-top, brainless, round the bend, screwball, crackbrained, moonstruck, whacky, nuts, of unsound mind, senseless, fruity, cockamamy, buggy, maniacal, bubbleheaded, loco, roughened, cockamamie, childish, loopy, off, non compos mentis, soft, mad, bedlam, inept, bananas, goofy, kookie, lunatic, certifiable, ludicrous, mad as a hatter, psycho, wud, wrong, dippy, alligatored, yeasty, mild, weak-minded, bughouse, bats, gaga, meshuga, preposterous, unhinged, screwy, nutty as a fruitcake, touched, mentally ill, simpleminded, fool, around the bend, brainsick, featherheaded, nutty, tomfool, batty, ridiculous, cockeyed, stark raving mad, zany, cracked, unwise, unsound, half-baked, sick in the head, loony tunes, nutlike, laughable
insane (part of speech: adjective)
- Mr. Watson probably thought that this young man was daft, but it was not his business to say so; he took down his erratic customer's address and said that all his instructions would be attended to forthwith. - "Prince Fortunatus", William Black.
- What richt had ye to luik at me, And drive me daft and dizzy? - "Alec Forbes of Howglen", George MacDonald.
- Here's a daft thing I'm doing for ye! - "Between You and Me", Sir Harry Lauder.