Schizophrenia?!

Have you ever met someone who treats you his/her best friend one second, and treats you like crap the next second? I have met a couple of these types of people. They can be very warm especially on the phone or on the net, but when you come into them by conincidence, they can just ignore you totally. For me, their behaviour is really unintelligible and uninterpretable, so I somehow suspect these types of people suffering some kind of mental diseases like schizophrenia and they really need to turn to a specialist for professional help. If their mental conditions are totally healthy, then these people are definitely very insecure or egocentric. They approach someone when they are in need (both practically or psychologically) and ditch right afterwards. What's wrong with these people? They really think others are idiots and their fake smiles and masks are THAT deceive enough to work all the time, even after they have done the same old trick over and over again?