And given the human tendency to generalize from one example, it has to be hard to take another look... My own learned response is 'the person is clumsy and so has to be ignored if possible; it does not matter why s/he is so, since both a mentally ill or just careless can probably realize my rudeness if I stare.' On the other hand, if someone at my workplace has a disability, I would be very wary of them having to do anything with volatile chemicals, and quietly but unceasingly influence things to make her/him stop. (I am in a plant physiology Dept.) Possibly I would be most rude to such a person, but exploding centrifuges just aren't safe.