Well, I encounter quite a few people like you throughout the week. One likes to make gestures as he talks to himself, and a few weeks ago my friend called the cops on him because the guy got all dressed up in his best clothes and stood out in the middle of a busy intersection to direct traffic. The police got him to a treatment center to get him back on his lithium, and now he's doing much better.
Another guy had spent half the night at the gas station pretending to talk on his cell phone. I had a very interesting conversation with him and recommended he read "Ironweed" by William Kennedy, which also became a movie with Jack Nicholson and Meryl Streep. He's always hanging out in the downtown library so it should be easy for him to find. His problem is that he couldn't cope with the death of his mother and spent three years doing meth. Now he's pretty much off of it and trying to do outreach with all the people he got to know on the streets. But unlike you, he's actually both coherent (mostly) and friendly, except for earlier that night when he was waving a knife at a clerk from Marathon, which got him in a little bit of trouble with the police.