The beginning of the words of his mouth is foolishness: and the end of his talk is mischievous madness. The beginning of the words of his mouth is foolishness: and the end of his talk is mischievous madness.
Illustrating the folly and injuriousness of the fool's words; last clause of Ecclesiastes 10:12.
Mischievous madness - "mischievous" first to others, then to himself, in just retribution.