How do you respond when it seems that your harasser has a mental illness?

How do you respond to harassment when it seems that the harasser has a mental illness or cognitive disability of some kind? I was just on my way into the laundromat with an arm load of laundry. There was a guy sitting on a bench a couple of stoops down. He called out to me, but I couldn't quite tell what he was saying. I made eye contact and gave him the same nod and half-hearted/half-guarded smile that I give to every male stranger as well as every acquaintance that I don't care to speak to. I continued on into the laudromat, and as I turned my back to him in order to enter the building, he called out to me again. Again, I couldn't quite tell what he was saying, and I just continued into the building. When our eyes met, he seemed benevolent, so I wasn't anxious about him. I put my laundry in the wash, and then walked out to go do errands. He called out to me again as I was crossing the street, and I noticed that he had some sort of make-shift cast/brace on one of his feet. The laundromat is in the same block with the place you go to get disability money if you are a veteran. Again, I couldn't tell what he said. I put my hand up, more in a stop sign than a waving sign, and just said hello loudly and nodded as I got into my car. I understand this may have been mixed signals. Then as I drove passed him, he made a disapproving/mischievous face and waved me to come over to him. This is when I started to feel harassed. I suppose people with disabilities and mental illness need to learn that harassing strangers is not okay just like everyone else does and that assertive communication is still a fine route to take. I just feel like a bit more of a jerk for not giving more slack to people who have a bit harder time in life, and I'm interested to hear what other folks think. I decided that if he called out to me again when I went back to get my laundry, I would walk toward him and ask him what he wanted, then make some statement about how continuing to call out to strangers when they're clearly not interested in speaking to you is harassment and not okay. When I went back, he had moved a block or so down the street and didn't call out to me. I didn't go to talk to him, but maybe I should have.

Happened on August 19, 2014

Incident reported by target

Bystander Action? No

Harassment Types: Sexual