To vituperate is to speak or write in an extremely negative way about someone.
Just as vituperation consists of negative, explosive, malicious outbursts, to vituperate is to communicate in this way. Negative political ads vituperate against opponents. When you insult someone and swear at them, you vituperate. People with a short temper tend to vituperate often — it's similar to railing, vilifying, and reviling. The root word is the Latin vituperationem, "blame or censuring," from vitium, "fault or defect."