An interesting article here, and a helpful list of words to use instead.
Using the word crazy as an insult is more harmful to the millions of us who deal with the stigma of mental illness than it is to the person you’re attempting to insult. It also lets the person/people you’re trying to insult off the hook by giving them an explanation for their erratic behavior or words rather than making them own what they said and did.
ignorant (see also: willfully ignorant)
And a contribution from across the pond in Ireland: “acting the maggot” and “gombeen.”