Although it's unknown what it actually stands for, this rather painful injection is given to Scottish children around the age of 13. As the injection site quickly develops into an extremely painful, puss-filled giant boil, many people without BCG's find it funny to hit people on the arm as hard as they can. However, this can backfire, rumours have circulated of the boils squirting pus over their attacker's fist.
Kid without BCG - "Waaaaaaay!" *hits kid with BCG on arm*
Kid with BCG - (screaming in pain) Aaaargh, my fucking BCG! Shit, shit, shit!
BCG... Back Croud Gack. Commonly used in large gatherings with associations of squires, fellow sir's and those of the same descent, being gacked. When tiresome has risen, and come down anxiety has arrived, BCG is calling your name.
literally, Birth Control Glasses. The glasses issued to new recruits in the military, so called because no girl would want to have sex with men wearing these ugly, ugly glasses.