The sudden change in atmosphere, when people are at the verge of aggression. In a crowd, in a store, in a bar, for example. I feel their conversation's shifting tone, the air becomes thick, and my stomach pulls into a solid knot.
I manage by leaving the vicinity. If that is not an option, I try to cause distraction. By changing the subject, if I am part of the exchange, by pointing out an object, a person, an interest and making a remark that requests a reply. I focus on emitting positive vibes myself and mentally try to relax myself and the situation.