IPA: //vɪˈtjuːpəreɪtə//
KK: /vɪˈtjuːpəreɪtə/
A person who criticizes or insults someone in a harsh and abusive way.
The vituperator shouted insults at the speaker during the debate.
Vituperator is formed from "vituperare" (meaning to blame or censure) and "-tor" (meaning one who). The word refers to one who blames or criticizes.
Think of someone who 'blames' ('vituperare') others — that's why a vituperator is someone who criticizes.