The act of writing on someones facebook wall to make either yourself or your friend seem more fun/cool/witty/popular. It is often done with the intention of someone in particular reading it.
Q: Why did Sarah write that on Janes facebook wall rather than just text her?
A: She was obviously peacocking
Jane: I really want Max to think that I am moving on!
Sarah: Don't worry, I will peacock you later about last night
Excessive displays of upper body flesh, by men, at inappropriate times in an effort to show off a new fake tan, a new roided up body, or a new trendy tattoo (i.e. barbed wire or Chinese power symbol); originated in homosexual communities, but is now commonly practiced by "alleged" heterosexuals at concerts, festivals, and other even more inapproprate settings.
It's 40 degrees, but those New Jersey pricks are still peacocking around in jeans and no shirt. It's curious why a man would be peacocking at a Pantera concert... there aren't even any women here.
When a girl unwraps her toga at a toga party so that the back of the toga is still attached to her by her belt; she uses said unwrapped toga to attract a mate or dance partner by wagging it in a suggestive manner.
Sarah: Where is Hayley?
Carrie: She is peacocking with Julius Caesar!!!
When a guy, traditionally with a big nose, puts his nose into a women's vagina until she orgasms. This usually involves some sort of nose plug and must be performed by someone who is able to hold their breathe for long periods of time.
Guy: Hey Guy 2 how'd it go with Sarah last night?
Guy 2: Oh it was great. She let me peacock her.
Guy: Dude that's Awesome! I wish I was you, but I don't have a big enough nose for peacocking, anyways.