It all started with the word safe. One lunchtime, after I'd kept a boy back for some now forgotten misdemeanour, I was telling him he was in danger of dropping down a set if his work didn't improve. He said he didn't want to move out of my class, because, in his words, "You're safe, Sir."
Since I didn't want to reveal my ignorance of the language of the corridor, I muttered something inconsequential and sent him on his way. But later I relayed the conversation to a cousin of his a couple of years up the school, and asked him what on earth safe meant. He smiled and took pity on my naivety. "That means you're OK, Sir. He likes you." Since then, I've kept a weather ear open to this word's usage and logged a number of descendants. "He's well safe." "She's the safest English teacher in the school." "He's safer than the last one."
And there's an important bit of body language that often goes with this: the clenched fist. But it's a gentle, reassuring fist, proffered towards the speaker in a peaceful fashion. It often, also, meets another one belonging to a contemporary, in a low-speed, mid-air, chest-height collision.
Safe comes from the same stable as heavy and bad. At the end of one lesson on geometrical drawing, I heard a 15-year-old compliment another on his work in these terms: "Hey Craig, that's heavy." A few months previously, I'd been told that a night out for another group of lads the same age was "really bad". I sympathised. "No, Sir, that means it was well good."
Some of this teenage vocabulary has a life span shorter than a housefly, but other phrases have a more enduring appeal. An example is the use of the word so. "I'm so tired," should be familiar to all generations. But then recently we began to hear "I'm so running out of time on my coursework", and "this is so my last exam". Only in the past few months, though, have the following constructions come right out into the open: "I'm so not seeing him tonight." "She's so not going to persuade me."
But you've got to be at your sharpest to pick up the exact message in some of the short one or two-word responses, the complexity of which are at their most potent at that charming age of 14. Teacher: "Have you written your homework down?" Pupil: "Whatever!" Teacher: "What does that mean? Yes, of course? No, but I'll remember what it is?" "Choose your answer. It's break and I'm out of here."
Stephen McCormack is a writer and supply teacher in London