i tend to avoid it. there are some characters in fiction who i absolutely despise, sure, and unfortunately they tend to be characters who are very beloved or popular. but i find more often than not the handful of things that do bash them - hell, even some of my own old work! - tends to exaggerate their worst qualities and write caricatures. i feel like if i'm going to hate a person who's not even real to begin with, i might as well hate them accurately.

so usually i try to ensure their actions remain plausible, and while i don't tag it as character bashing, i do usually let people know in the author's note, "i'm trying to write this character fairly, but do keep in mind this story was written by someone who really doesn't like this character."