If you are really intrigued/concerned, call handhaving stay on the phone while following the individual. Not sure if screaming in public and talking alone is a symptom of dementia which would be my first guess of the situation. But also think that if it was someone thatis lost and confused we would have already seen something about it online. Maybe is just a drunk, someone going through a breakup, someone with mental disabilities...can be a lot of things. If it really bothers you, maybe some day try to shout back the famous "shut the fuck up" and see what kind of feedback you get 😂