תהילים נ:כ פירוש: רש״י

You sit in the company of the scorners.

your mother’s son with whom you have no [legal] quarrel, since he does not inherit with you.

slander Heb. דפי, defamation to cast him off, an expression of (Num. 35:20): “he pushes him off (יהדפנו).”