He who doth not perform the Sraddha for the Pitris, nor worshippeth the deities, nor acquireth noble-minded friends, is said to be a person of foolish soul. That worst of men who entereth a place uninvited, and talketh much without being asked, and reposeth trust on untrustworthy wights, is a fool. That man who being himself guilty casteth the blame on others, and who though impotent giveth vent to anger, is the most foolish of men.

In plain words: A fool does not honor his ancestors with the Sraddha ritual, does not worship the gods, and makes no good friends. He goes where he isn't invited, talks too much unasked, and trusts untrustworthy people. The biggest fool blames others for his own mistakes and gets angry when he has no power to act.