Definition 1: Defame, malign, utter slanderous statements against someone. The noun is "vilification".

Usage 1: A clear indicator of how we can lose our sense of language is the recent emergence of the term "bad-mouth". This compound verb suggests a curse of bad breath more than vilification or defamation.

Suggested usage: Here is a much more poignant term for expressing the same idea as "bad-mouth": "How could you vilify me like that for accidentally locking the key and the dog in the car?"

Etymology: A verb derived from Latin vilis "cheap, common, worthless" (from which vile also originates).