We've all been there. Falling in with bad company and then living to regret it seems to be part of the human condition.
Whether it's an ill-advised alliance with the Conservative party, your best man or that bloke you met in Morrisons, it shows an error in your long-term judgment.
Hanging about with the wrong sort is a rite of passage and one that teachers witness on a daily basis. One minute Lovely Lauren is skipping off to her flute lesson, all righteousness and Wright's coal tar soap, the next she's sloping off to the bog for a quick fix of foundation and a furtive play on her iPhone.
And the transformation is nearly always triggered by changes in her group of friends. Eager-eyed teachers get used to tracking these developments: her home-work and skirt shrink at the same alarming rate, her class work staggers to a halt, and everything within her gravitational pull - books, file paper, and small classmates with August birthdays - get smeared in toxic orange make-up.
To be honest, the chances of Lovely Lauren coming out of her schooling unscathed were always going to be slim. Mixed-ability teaching means we roll out challenging behaviour like some kind of HIB vaccination, where we inject a small dose of unruly pupils into the main student body with the hope they will eventually be neutralised by the prevalent army of healthy, freshly scrubbed antibodies.
It doesn't always work that way; as with most immunisation programmes, there's a risk of collateral damage. For every naughty kid we convert to the chess club, there's a kid with RP and a double bass who starts nicking padded bras from La Senza.
But what constitutes "bad company" can sometimes be a matter of context. Here's a key example: while PE teachers are great to have on a pub quiz team, you should avoid them like the plague during Inset. They are not renowned for curbing their impulsivity and their tendency to punctuate the principal's whole-school address with derisive snorts can attract attention.
The problem is that their disapprobation is never subtly manifested; what sounds like a hushed whisper to PE staff reverberates like an airshow tannoy to the rest of us. If in any doubt, sit next to the DT department on the basis that you are seldom compromised by people who are half asleep.
Sometimes we end up being the bad influence without realising it. Thanks to my mother, an aspirational bookies' clerk, I had a Lawrentian childhood, but with less visceral introspection and more Bird's instant trifle. As a result of her throbbing ambition, I ended up with a scholarship to an all-girls' school. Before I enrolled, I had been under the illusion that we were quite posh: we were the first in our street to buy Ski yogurt off the milkman or taste the desiccated Eastern promise inside a box of Vesta chow mein. But social class clings to you like the smell of fish because the only girls who came back for tea were the other two scholarship kids.
And now, the internet has opened up exciting ways of mixing with the wrong sort. Over the past few months Facebook has been fortifying the over-forties to such an extent that three of my friends' husbands have abandoned them for smoother, less pixellated alternatives. And who can blame them? They can now poke away to their heart's content and no-one's asking them to put away the dishes.
Anne Thrope (Ms) is a secondary teacher in the north of England.