Suddenly the school looks like a meeting of the Angry Club at a dyslexics convention. FCUK? Year 9, set 6, believe that’s how it is spelt now. They can’t even swear at me and get it right. Soon I shall be correcting graffiti.

The logo has become a knowing act of defiance. I know what it means. They know what it means. But to make an issue of it makes me look foolish. So all I can do is sigh as our language and our culture is debased to sell clothes.

Middle-aged, middle-class teachers like myself can disapprove. But we are swimming against the tide. Where swearing is the common currency of the home, we are requiring our children to adopt a very sophisticated code of behaviour. Different vocabulary in different situations.

Where there was once some vague parallel between the classroom and home, now the connections are between the home and the playground. And sometimes the kids can forget the rules. They can respond instinctively in class and then I have a problem. Because it is directed at a teacher, swearing is an act of aggression. Teachers are affronted. They are violated and demand retribution. “Don’t you use that language in my classroom! You don’t say that at home!” Well, actually they probably do.

To swear confidently persuades some of my scholars that they are acting in a mature and adult way. I might say that it reflects a lack of vocabulary, but to them it is a passport to the world of working men with a knowing skill and a box of specialist tools. Swearing, sucking through your teeth, and saying that your big end has gone is what grown-ups do.

Most exclusions we deal with are for swearing at teachers. Sometimes we must all become diplomatically deaf, but other times that isn’t an option.

If a class is watching, you must react. You can’t be seen to give a licence for such language. And the students themselves are in control. In fact, they can determine when and for how long they are excluded.

The words they select carry an unspoken tariff. Like Olympic divers, they can go for the complicated double “eff” with a piked “c” which, when executed properly, will let them enjoy daytime television for a week. An unambitious “bastard” and you get to sit outside my office for a while, top whack. And maybe miss maths.

Pupils also know that we are not supposed to use these words. I am always amused when my trainee villains return from their NVQ courses in motor mechanics or building. They will come rushing to me, outraged that an impatient instructor has directed the common linguistic currency of the workplace at them. “He can’t say that! He’s a teacher!” Perhaps our off-site colleagues have an advantage over us. Certainly, I can sense it in the voice of the angry teacher. They shout red-faced at the naughty child and underneath it all their minds are working overtime to seek out an acceptable vocabulary, while all the time there is a burning itch to spit out an expletive. No wonder teachers in a rage tail off into incoherence, seemingly exhausted by their mental gymnastics.

The forbidden words are far more accessible. The “f” word has lost some of its mystery and power. It is used more frequently. It can sprinkle even the politest conversation. But there is still an ultimate taboo. The “c” word still has the capacity to horrify. It is still a step too far. For the moment.

The language eats away at you, erodes standards. Now everything is “crap”.

A word I would never have said in the presence of my mother is so common in school that it is unremarkable. In school you develop an unrestricted familiarity with an industrial vocabulary. It is not a place for a shrinking violet. It is full of kids trying to sound hard and uncompromising. Swear enough and you will begin to believe you are. If you can talk it, one day you might be able to walk it, given time.

But it is boring. Same words all the time. Just once in a while I’d like to be abused with a bit more imagination.

Geoff Brookes is deputy head of Cefn Hengoed secondary school, Swansea