A face to express annoyance, sarcasm, or frustation. It can fit many situations, really.
It is a sort of wink but more of an angry/annoyed wink; not a flirtatious wink. It can be kind of a way of making the other person feel like an idiot when they don't know what they're talking about or state something obvious or even false. The user can be implying they know something the other person(s) does not.
A: "Hawhaw! You're short." <-Idiot
B: "Naw. -.O" <-Sarcasm
A: "Omgigawd! I'm so cool. :]"
B: "-.O Mhm, sure you are."