So there's this chick in my office with whom I started to develop a friendship - and then sometime around March she completely shut down, stopped talking to me, and after having a conversation with her she explained that she just wanted to focus on her work and didn't want to socialize. Which is fine, though I had what I thought was a reasonable expectation of civility in the work place. If someone does something for you, say thank you. If someone addresses you (as in, for work related things), acknowledge you've been spoken to.
She did none of those things. I would relieve her for her breaks and there wouldn't be so much as a thank you. I would ask her direct questions regarding work related things and she wouldn't acknowledge my presence. And yet somehow her "no socializing" rule would seem to bend with other people in the office.
I finally decided to ask my manager about it, noting that I felt I was being a little high school for the complaint, but that it was subtly hostile working environment and worth addressing. Much to my surprise, she was extremely receptive (I think she's suspected this issue) but told me with surprisingly glee that the co-worker's last day is this Friday, as she has handed in her notice.
All's well that ends well!