A fool; an unintelligent or imprudent person (somewhat literary and often pejorative).
人を傷つける言葉を平気で言うのは愚人のすることだ。
Saying words that hurt others without remorse is something a fool does.
愚人と呼ばれるのは嫌だが、行いを改める必要がある。
I don't want to be called a fool, but I need to change my behavior.