piitb is from an unknown origin but gained popularity on MustangWorld.com throughout the late 90's and into today.
User 1: Hi, im Brian Peppers!
User 2: O'rly?
User 1: I got in a fight at my grans and mum said your moving with your uncle and auntie in belair.
User 2: I saw that coming.
User 1: Are you aware that I saw that comin
User 2: You see your focusing on thing that arn't important in life...
User 1: Piitb? (no homo)
naret notsag: Did you piitb?
myself: Oh, DID I!!