Kevin -- I've worked with that patron too - when I last saw him, he didn't seem dangerous but he did seem to be inhabiting a different reality from mine.

I've been getting a couple of rude or abusive middle schoolers nearly every week. I'm starting to give one warning, then disconnect -- I used to try to give more warnings and just not react to the inappropriate stuff. Now I'm trying to remember that if I accept abusive behavior, I'm also teaching patrons (especially young patrons) that it's okay to cuss the librarian out. Not what I want to encourage!