"Reen" is a shortened version of Pipareni (Pie-pah-ree-nai) and is part of a newly emerging language created by recreational drug users similar to cockney rhyming slang but from the North East of England. Using this language, it is easy to talk about anything illegal and not let slip any details. A Pipareni is simply a pipe, through which various forms of cannabis are smoked. The term was originally created by HSH
"Ha'weh lads, wa gaan fo a reen"
"Aye, av got Stanger
next n it's fuckin wank. Let wi' gaan fo a reen"
"Fuck it, have a reen"
Reen is the term used to describe any boy with a birdlike appearance. Qualities seen most often with these are large heads, fluffy hair, various nicknames such as "Reenis the penis" "Bird" "Furby" "Devil Boy", a large mole, and much tormentation from classmates.
Move out of the way Reen, I can't see anything with your birdlike head in the way.