Generally, I do not run into too many people who may have mental issues when I ride the train in Chicago. At least not on the train line I am on 99% of the time. Last night however, I did encounter what can only be described as a woman who has some problem.
If you are unfamiliar with the El trains in Chicago, most of the stops on a given line the doors will open on one side of the car or the other. On the Brown line, they usually open on the right with a few exceptions. If I do not get a seat or just feel like standing, I will stand by the doors on the side of the car where the doors will not be opening so that I am out of the way. I did this last night like I normally do.