[_delirium]

Defamation per se is very limited under the First Amendment, and mostly historical at this point, dating from an era when courts would entertain prosecutions for calling someone's honor into question. To the extent it survives, it's been limited mostly to where "regular" defamation would also apply, to false statements of fact. For example, "injurious to another in their trade" can't be used to prosecute any comment that could harm someone's business, but only false factual statements that could do so, such as accusing someone of selling counterfeit parts. Nowadays the only real distinction is in showing damages: in a per se category, once defamation is proven, the plaintiff doesn't have to further prove that they were harmed, because harm is assumed in those categories.

I think mostly we're discussing something else here, angry and vitriolic "piling-on" responses, which is a different issue from defaming someone.