What to do?

F line/ going to art supply store: Normally I welcome the diversity of the bus. I think it's good for Leila to get exposed to all walks of life, and riding the bus certainly exposes us to all sorts of people. However, sometimes I get a bad vibe. We were waiting to board the bus and this guy was standing a little to close for comfort. He hadn't bathed in a while and was vigorously chewing his nails and looking our way. I didn't pay him much attention till he started grumbling. Now, I have seen some mental break downs on the bus before, and they ain't pretty. I certainly don't want to be caught in the middle of one with Leila. The grumbling quickly turned into cussing, something about a toilet, feces and a friend of his. So, what's the protocol here? I chose to wait it out, but as Leila gets bigger, I am not sure what the best move is. Do I move away? Wait and see? I am not one to say something, especially if the person is agitated. Tough call. Thoughts?