WordNet (r) 3.0 (2006):

screwy
    adj 1: not behaving normally [syn: screw-loose, screwy]

Moby Thesaurus II by Grady Ward, 1.0:

123 Moby Thesaurus words for "screwy":
   abnormal, anomalous, apish, asinine, balmy, bananas, barmy, bats,
   batty, beany, befooled, beguiled, besotted, bonkers, boozy,
   brainless, buffoonish, buggy, bughouse, bugs, canned, cockeyed,
   cracked, crackers, crank, crankish, cranky, crazy, credulous,
   crotchety, cuckoo, daffy, daft, dazed, deviant, deviative,
   different, dippy, disguised, divergent, dizzy, doting, dotty,
   drunk, dumb, eccentric, erratic, exceptional, fatuitous, fatuous,
   fey, flaky, flipped, fond, fool, foolheaded, foolish, freaked-out,
   freakish, fruitcakey, fruity, fuddled, funny, futile, gaga, goofy,
   gulled, haywire, idiocratic, idiosyncratic, idiotic, imbecile,
   inane, inebriated, inept, infatuated, insane, irregular,
   just plain nuts, kinky, kooky, loony, loopy, lunatic, mad, maggoty,
   maudlin, moronic, muddled, nuts, nutty, odd, oddball,
   off the hinges, off the track, off the wall, peculiar, pixilated,
   plastered, potty, queer, quirky, round the bend, sappy, screwball,
   screwballs, senseless, sentimental, silly, singular, slaphappy,
   strange, stupid, thoughtless, twisted, unbalanced, unconventional,
   unnatural, unsound, wacky, wet, whimsical, witless