insanely irresponsible; "an idiotic idea"

completely devoid of wisdom or good sense; "the absurd excuse that the dog ate his homework"; "that's a cockeyed idea"; "ask a nonsensical question and get a nonsensical answer"; "a contribution so small as to be laughable"; "it is ludicrous to call a cottage a mansion"; "a preposterous attempt to turn back the pages of history"; "her conceited assumption of universal interest in her rather dull children was ridiculous"

Pertaining to, or like, an idiot; characterized by idiocy; foolish; fatuous; as, an idiotic person, speech, laugh, or action.

having a mental age of three to seven years

Common; simple.