Means: A cigarette
Usage: "Sort me a blem, Danny"
While school kids smoking behind the bike sheds is something of a sepia-tinted institution, its connected language changes all the time, adapting as every new generation of teacher becomes more adept at spotting the behaviour and terminology connected with such a flagrant abuse of school policy. Blem is the latest cloaked term for the humble fag, derived, somewhat inevitably nowadays, from drugs culture. There it is used to describe the joint itself, as well as an adjective for being high ("I'm so blem, mate"), where it is thought to be an abbreviation of "blemish", in that marijuana impairs your ability to ... well ... erm ... do stuff.