I don't get why anyone who rides public transportation doesn't wear headphones themselves. Big obvious ones are best so people don't talk to you.
I do find that the more righteous I feel about someone's actions the more annoying it becomes to me. Despite how rude it is, and you're absolutely right about that, try to not give a fuck. It really helps to consider their obliviousness as a disorder. They're pathetic.
If nothing else, hopefully it'll keep you from actually pulling the trigger one day.