Anon, the short-form version of the word "Anonymous" is used to refer to those who access the internet with so-called "anonymity" and participate in actions that aren't tied to their real name.
Being an AnonO_o means that you possess said anonymity, but however are shockingly beautiful. Although, with possessed anonymity you are merely pixels, to other anonymous persons you are the stunning beauty that causes them to go "O_o"
When I was on irc today, I met an AnonO_o, damn, she sounded hot. or I was so shocked at the beauty of that Anon, I thought she must be an AnonO_o.