You can tell by body language and behaviour what they think/feel about/towards you in a situation and in general how they are towards you. But you can't tell what they tell ABOUT you to other people, as @pericles said.
This may sound weird, so it was for me and I was pissed about it when I first encountered such a thing. In fact I was not pissed about that they made me demonic person in other's minds, but that they weren't able to tell straightfoward to me what their problem is.
and sadly marty, there are people who you can't just avoid. Co-workers, school mates, close family. You may decrease contact to minimum but they will remain and BS about you behind ur back.