When you walk into the office on April 1, you may find something amiss. If you have a reputation for excessive tidiness, perhaps everything on your desk has been moved by a couple of centimetres.
Maybe someone has switched your PC screensaver to a fake "system error" screen. If you are particularly unlucky, a mobile phone may be taped to the underside of your desk, while colleagues wait to ring in and watch you scramble in vain.
The April Fools' day gag is a long-standing tradition in many of the world's workplaces. Instances range from the simple placement of a whoopee cushion to the surreal and ridiculous company announcement, fully sanctioned by managers.
One was carried out by Burger King in 1998, when it took out a full-page advertisement in USA Today announcing the launch of the left-handed Whopper: "After years of neglect, left-handed eaters will no longer need to conform to traditional right-handed eating methods."
Thousands of customers ordered the lefty Whopper, but most saw the joke and the burger chain reaped favourable publicity.
BMW has a proud tradition of the annual spoof ad. Memorable efforts include collectable porcelain BMWs, steering wheel free cars and a horn whose sound calms rather than enrages other motorists. "It just shows a different side to us," the company says. It notes that the ads appear only in the UK: "The British sense of humour is rather particular."
Perhaps the best known corporate prankster is Google, whose public announcements range from ads for jobs in a research centre on the moon (2004) to finding love ("Dating is a search problem. Solve it with Google Romance.").
Individual pranks can be rather more risky than those agreed by management. One media planner recalls sending an all-staff memo at his New York ad agency announcing the start of random drug testing.
"Widespread panic ensued, especially among the lower ranks," he says. A reprimand from the company president was swift to follow.
Adrian Gostick, co-author of The Levity Effect: Why it Pays to Lighten Up, says April Fool gags tend to work best in companies with a fun culture rather than businesses that loosen their ties once a year. "Organisations should take fun seriously. In the [leading companies in] a Fortune survey of Best Places to Work, we found a dramatically higher percentage of people who said they had fun at work."
Sarah Sweetman, senior partner at Organisational Edge, the business psychologists, believes great practical jokes can even help to shape corporate identity. "April Fool jokes can become stories that are repeated years after they happen."
The problem is that the stories with the longest legs are not always those a business would like to remember.
It is a question of degree and context, says Michael Burd of the law firm Lewis Silkin. "Few would object to minor, harmless, one-off pranks done in an appropriate spirit. But something that is seriously embarrassing or humiliating to a fellow colleague, or potentially damaging to the organisation, can be a big no-no."
The consequences of pranks gone wrong range from discomfort to disaster. In How to Lose Friends and Alienate People, author Toby Young related how he brought a strippergram into Conde Nast's New York offices to embarrass a colleague on his birthday, only to discover that it also happened to be "Take Our Daughters to Work Day". He was saved because his transgression was "so galactically inappropriate people didn't know what to make of it", he wrote.
In the case of Glenn Howlett, community services manager for the city council in London, Ontario, the outcome was less happy. While he was on holiday colleagues sent him a joke memo saying he had two weeks to present a major report. He cut short his break, rushed back, suffered from heart palpitations, was put on fully paid leave for stress and eventually negotiated a costly early retirement package. The city now has a by-law prohibiting its employees from playing practical jokes at work.
