"Sling off" can be used to describe the act of insulting or speaking rudely to someone. Here are some synonyms for this term: lash out, hurl insults, verbally attack, berate, criticize, condemn, malign, belittle, disparage, denigrate, castigate, rebuke, admonish, reprimand, scold, chide, upbraid, reproach, censure, and condemn. These words are useful for writers, speakers, and communicators who wish to explore different ways to express negative language or critique others. However, it's important to use them with caution and considerate not to offend anyone or cause unnecessary harm.