2) to do something quickly and appear to be an idiot because you didn't think beforehand. Possible when reacting by reflex or when startled.
3) (archaic) to use a catch-phrase or cliche in a really stupid way because you are an idiot. Similar to "idiomatically," but with a lower IQ.
2) So Joe jumped out from behind those bushes last night and scared the crap out of me; I idiotimatically tried to hit him with the half-empty case of beer I was carrying, scattered beer cans all over the street.
3) "That's what she said."