To be or become wild, restless, irrational, or insane; to act in such a way. The drivers in this country seem to go completely zonkers if there's even a little bit of snow on the ground. Don't give the kids too much sugar or they'll end up going zonkers! We thought taking our family vacation in a tiny cottage out in the country would be a nice break from city life, but we all went a bit zonkers after a few days.