I've been to a lot of parties that have devolved into messes. I'm not a fan. I don't prefer to go to parties that don't include people I'm related to.
Vomitting from others
There's a good chance that I would feel obliged to help clean up the mess if it was one of my friends that was sick or it was one of my friends house.
Whether involved in the fight (or shouting match) or just present when it starts. It's best to head out either way. Then you aren't the crazy yeller OR the observer.
General presence of crazies
I'm just not a fan of crazies.