fling (or sling or throw) mud make disparaging or scandalous remarks or accusations. informal
The proverb throw dirt (or mud) enough, and some will stick , to which this phrase alludes, is attributed to the Florentine statesman Niccolò Machiavelli ( 1469–1527 ).
fling/sling/throw ˈmud (at somebody) (informal) try to damage somebody’s reputation by telling other people bad things about them: Just before an election, politicians really start to sling mud at each other. ▶ ˈmud-slinging noun: There’s too much mud-slinging by irresponsible journalists.