Guyana: Don't stop hooting/honking.
Guyanese drivers seem to be leading the worldwide revolution in car hooter functionality. Not content with it as a vaguely obnoxious, sometimes-necessary warning tool, they have used it to develop a complex, quasi-SONAR system of urban navigation – where you hoot to let others know when you're taking off, when you're turning, when you're overtaking, and when you're approaching an intersection (really blast the thing, if you're not planning on stopping). If you ever find yourself behind the wheel on a Guyanese road, unless you want to be invisible, don't let up on your hooter.
Singapore: Don't chew.
Although somewhat of a cliché by now, Singapore's famous ban on chewing gun merits inclusion in this list, if only because of the (quite adorable) steadfastness of their position on the issue. Eighteen years of international incredulity (not to mention, significant teasing) led to a referendum on the matter in June 2010 – when government officials decided to 'stick' to their proscription of the corrupting chew, prompting wild celebrations on the part of train seats around the city.
Mauritania: Don't... do anything, really.
A veritable land of 'Thou Shalt Nots', it'd probably be shorter to make a list of the things you CAN do in Mauritania... Nevertheless, topping the list must be its draconian stance against public displays of affection between men and women. Not even married couples are permitted to hold hands in public in Mauritania – which might go some way toward explaining it's relative unpopularity as a global honeymoon destination. Another oddity: in public, women can't lie on their backs, and men shouldn't lie on their stomachs.
Micronesia: Don't you rub your belly like that, I know what that means....
Hungry? Full? Feeling queasy? Need to tuck your shirt in a little more? All these good reasons to rub your belly, but in Micronesia, they're the equivalent of putting on your best fishnets and hanging out on a street corner by the docks after nightfall. That's right – in Micronesia, if you want to let someone know that you're, um, interested, the quickest way would be to give your gut a little rub in their presence. Gastronomy-themed pick-up lines are optional.
North Korea: Don't mention that gigantic skyscraper over there.
Taking the idea of an 'elephant in the room' to its absurd conclusion, North Korea's abandoned Ryugyong Hotel in downtown Pyongyang – a 105-storey, pyramid-shaped concrete affair, once called “the worst building in the history of mankind” by Esquire magazine – is curiously absent from all official photographs of the capital city. And while 'disappearing' things from photographs wasn't invented by North Korea, the public's herculean act of 'double-think' has ensured that even while in Pyongyang, it's hard (in fact, potentially hazardous) to get anyone to admit that the building actually exists.
Construction started on the Ryugyong Hotel in 1987, with builders giving themselves the optimistic target of completing it in 1989 (at which time, it would have been the tallest hotel in the world...and definitely still the ugliest). However, in 1992, pesky construction problems, such as crumbling concrete, and sagging girders, significantly stalled the project – before it was totally abandoned in 1996 due to a lack of funds, electricity shortages, and widespread famine. A national embarrassment, and a monument to the bizarre workings of the North Korean government, if you ever find yourself in Pyongyang, fight your urge to compliment the skyline.
Image of Ryugyong Hotel from here.