what is the word for saying bad words about other people [duplicate]
scandalmonger :
One who spreads malicious gossip.
or:
slanderer:
Someone who makes a false and malicious statement or report about someone.
backbite
to talk spitefully about (an absent person)
And the person is a backbiter.
Backbiting may occur as a form of release after a confrontation. By insulting the opposing person, the backbiter diminishes them and, by doing so, restores their own self-esteem.