Grown men do silly things sometimes. Take the warders of London’s Wandsworth Prison who scrawled “We have Madeleine McCann” on their T-shirts on a boozy night out and posted the pictures on Facebook. This led to disciplinary charges against all those involved and one of them losing his job.

The fine line between what you do at work and outside of it is changing. Just as the Wandsworth warders’ ill-advised antics came to light, a tribunal decided that the racing commentator John McCririck had been shown the door by Channel 4 not because he was old but because he was a plonker. Or, to put it another way, a self-proclaimed bigot and sexist loudmouth whose “pantomime-villain persona” on Celebrity Big Brother was not going to win the channel new audiences.

This changing climate pervades education, too. Once, being a sexist loudmouth was one of the requirements for your appointment as a college principal. But no longer. We are now more sensitive to issues of gender, disability and race.

So what do you have to do to get yourself sacked these days? Things have got tougher around competence. When I was at school, the head of geography spent much of the time he should have been teaching us smoking cigarettes in the stock cupboard. Today, schools and colleges tend to use the competence procedures that have always been available to them, although some now think that things have swung too far in the opposite direction.

Another major no-no is sex. In schools, it’s straightforward: if you run away with your underage student, losing your job is of only minor concern. More problematic are the three or four years you’ll be spending at the mercy of those callous Wandsworth prison officers and their T-shirts. In colleges, however, it’s not so simple. Indeed, consensual sexual relations between staff and students come in 50 shades of grey (well, two or three, but the metaphor seemed too good to pass up). Further education lecturers are not banned from having relationships with those they teach, like doctors. And their students range all the way up to - and sometimes beyond - retirement age. Many lecturers of both sexes have found life partners from among their students.

But college managements are becoming increasingly less tolerant of such liaisons, branding them “unprofessional” and threatening disciplinary action over those discovered. Union advice on this topic is that if the “chemistry” develops, wait until the student leaves before initiating the first “experiment”.

Which brings us neatly back to social media. Here teachers have to be careful - more so than others. If Bill Bloggs in his office job puts up a jokey online image of himself wearing a party hat and seeming to smoke a crack pipe, all his mates have a good laugh. If Bill Bloggs the teacher does it, all hell breaks loose and the press has a field day with its “Sir the junkie” headlines. Instant dismissal will surely follow. Unless, that is, they decide to make you mayor of Toronto instead.

Stephen Jones is a lecturer at a further education college in London, England.