The rules that govern Vietnamese social interaction can appear a bit confusing for newcomers to the country, but the good news is that few people stand on ceremony, and most slips in etiquette will be forgiven if they are seen to be caused by ignorance rather than malice.
First and foremost, it is important to respect the authority of soldiers and police, as anyone who falls foul of the state is in big trouble. This shouldn’t be a problem in general and is only likely to happen if you should photograph a military installation or something similar, which could lead to your camera being confiscated.
Despite being a communist society on a superficial level, the traditional cultural determinants are Confucianism and Buddhism, which are generally quite tolerant. As long as you show respect by dressing conservatively when visiting religious building such as pagodas (this means no shorts or sleeveless shirts), there is little danger of upsetting the locals.
As in other Southeast Asian countries, it is also a custom to remove shoes before entering the main building of a temple compound, though this is not always adhered to, so the best advice is to keep an eye on the locals and copy them.
Also in common with other Southeast Asian countries, it is deemed improper in Vietnam to lose your temper and get angry about anything, and will almost certainly make any resolution to your problem less likely. So keep calm, count to ten, put on a smile and you are much more likely to find a solution to your difficulties.
The conservative element of Vietnamese culture is also evident on the beach, where nudity is not tolerated at all. In fact, most Vietnamese go splashing about in the sea fully dressed and are puzzled by the Western penchant for soaking up the sunshine while wearing almost nothing. As in most countries, single women need to be particularly careful not to give the wrong signals by dressing in a provocative manner.
Though generally accepting of eccentric behaviour, the Vietnamese are not always so tolerant when it comes to gay relationships. Though there are a few bars in Hanoi where gay people can feel comfortable, there are no establishments dedicated to homosexuals so a restrained approach is advisable.
Perhaps the place where most Western visitors feel unsure how to act is in a restaurant, especially if you are eating with Vietnamese. In this case, wait for the most senior person at the table to start first, then take a spoonful at a time from the central communal bowls, mix it with your rice in a small eating bowl and go back for more later.
In most places, bones and discarded tissues are thrown on the floor, but keep an eye on your Vietnamese hosts to be sure. Finally, when eating noodles, lift your bowl to your mouth (or drop your mouth to the bowl), shovel a few strands into your mouth with your chopsticks, and slurp away to your heart’s content.