Yeah Ive had this as I am sure everyone in life has at times. But yeah its very uncomfortable and depending how you're feeling in yourself makes a huge difference.
I tell you what really winds me up around this area though...
When people do it when the circumstances provide them that opportunity.
So say people are treating you OK to start but then they realise you're different. Now I dont always mean different in a negative way it could be because they think you're different in a better way like more naturally friendly or better skill wise, better looking etc. Or it could be the more negatives like they see you arent like them in being quiet or not conforming to the clique etc.
It doesnt really matter the reason and I understand that everyone isnt always going to be everyones friend or choice to socialise with. But the different would always be in a way thats different from their comfort zone.
When the circumstances are right i.e. that person is deemed vulnerable in some way. Thats when you notice some peoples true colors and they can be rude in a way that they never would normally. Or maybe I should say that is how they are normally and all the rest is an act.
That bothers me on levels more than just it being personal to me because it feels like you cant be yourself or show any weakness around a lot of people. I guess thats why people have cliques etc to have some security from this type of thing.