Ethics aside, in my experience this type of character tends to contaminate their surroundings with this undirected negativity. It’s like a black hole that has no sides, only the mass of their ego. I have a friend like this, and while we are still friends and can manage that, I would never work together with him. It’s okay to be sad, stressed, angry. Not okay to spill it all over the world.

Otoh, not clear what gp means by “rude”. Someone could perceive sad/neutral silence and “thank you, goodbye” as rude-ish too.