Comes from the awesome music video featuring Justin Timberlake and Andy Samberg which was shown on Saturday Night live.
The video rips the shit out of sex music of the early 90's. Its about two Cassanova men who attach boxes to their waists and have their dicks in the boxes. They then present the box to their lovers as a Christmas gift or any occasion for that matter:
'Christmas... dick in a box, Hanukkah... dick in a box, Kwanzaa... a dick in a box, Every single holiday a dick in a box, Over at your parent's house a dick in a box
Mid day at the grocery store a dick in a box...'
Some complete legends who live in southsea discovered this video and after watching it over and over it, the phrase dick in a box became abbreviated to DIAB and used as an insult.
Origin: Justin Timberlake and Andy Samberg made a short on Saturday Night Live. The music video is about two Casanova-type men who attach a box to their waists with their dicks in the box which is then given to their lovers as a gift for christmas. 1: "Cut a hole in a box", 2: "Put your junk in that box", 3: "Make her open the box...and that's the way you do it!" - Genious
Some legends who live in Southsea came across this video and thought it is the funniest thing EVER and after watching it over and over the word DIAB became used as an insult.
Kyle: Yeah i know, what a loser, that guy can't even make fun of people with A.D.D or he will just get laughed at for being such a stupid diab.