Three times on my commute around town on the subway, I've encountered people who are openly hostile for whatever reason, potentially drugs or alcohol or maybe just naturally violent. In two cases the person in question went around the train shouting death threats at people, pounding on the doors and windows of the train, and in one case spitting on people. The other was an altercation on the platform that again ended in someone being spit upon and an arrest by transit police.
The general reaction from people (myself included) on the train was to keep your head down, not engage, and wait for either this passenger to disembark or for transit workers to deal with the situation while praying you aren't targeted individually. Are there any other more constructive ways to deal with this situation?