There are a few people I see socially who I think just don't like me. They don't hate me, but whenever I see them, their eyes tell me that their smiles are fake. (Here's a good test to see how effective you are at telling.)
I wish it didn't bug me, but it does. Part of me wants to go up to them and just say, "hey, what's the deal?" Part of me says, forget about it.
It's just irritating when I have a suspicion that can't be confirmed.