What is //.o?
The emo emoticon. the two slashes // make up the infamous emo swoosh. the period makes the nose and the o makes the other, or perhaps, the emo's only eye.
// are is the emo swoosh
. is the one visible eye
and o is the emo mouth saying "Woe is me."
me: Go kill yourself
emo kid: //.O
me: dude, i totally banged your girlfriend last night