I have had this in the past with a friend and am now having it currently with another friend.
It's mainly on Facebook, although she is like it in person too. She is very sugary and sweet and nice to everyone else but comments very abruptly on my statuses and pictures and is quite abrupt with the way she speaks to me too.
I posted something a couple of days ago about a tv programme and her reply was "It's a tv show!" which I thought was rude, as of course I knew it was a tv show! I know that if other people posted a similar thing to me she'd be all nice in her replies.
She is also quite sarcastic towards me, and not to others.
Reading back through this I do realise it sounds ridiculous, but it's really getting to me.