When one says/does
something mean, that they would not normally do,
just because they're angry.
Generally unnecessarily mean in proportion to the level of anger. Often a symptom of being butthurt.
Girl 1: (joke)
Girl 2: Sounds like something my 7-year-old cousin would say.
Girl 1: Well, that sounds like something a 20-year-old with an
unfortunate face would say.
What is that, partial facial paralysis?
Girl 3: Dang, you get meangry quick. Girl 2 has a
cute face.