well...if you stiffen up with closer proximity and your facial features show reluctance, like you're uncomfortable, etc. than that would be one sign. When a person lacks sympathy or empathy there is a lack of concern in their eyes and facial features and they tend to turn away or stiffen slightly and make no movement towards the person. There are so many subtle movements though that vary from situation to situation that I don't think I can explain. Usually people just "know". although it is all body language. anybody have anything else?