idiotic
adj.
insanely irresponsible
an idiotic idea
Synonym: crackbrained
adj.
so unreasonable as to invite derision
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
adj.
having a mental age of three to seven years