Nightlife in Vietnam can be split into three different types: the local scene, the expat and tourist scene, and a hybrid scene for modern urban Vietnamese including some expats.
For locals, gathering at cafes, singing karaoke (or hugging karaoke om girls), "nhau"-ing at big outdoor "quan nhau", or just driving around and hanging out outside are common nightlife activities.
When it comes to clubbing, it's hard to tell how many nightclubs exist in Vietnam. This is because most of them are part of the local scene and don't receive many foreign customers and don't make themselves attractive to foreigners anyways.
A typical Vietnamese club is open every day of the week, opens in the evening, and closes at midnight. Customers are mostly Vietnamese males who come in groups and then stand around a table while female staff pour drinks from a bottle of liquor which the group has ordered. If they don't finish drinking the bottle that night they can check the bottle and receive a card to retrieve their bottle later. Sometimes, the bottle will be marked so the customer trusts that it is his bottle and that nobody else has drunk from it before he returns. But this doesn't ensure that the alcohol inside is not counterfeit. Counterfeit name brand liquor is a huge problem here, creating a secondary market for used bottles of vodka, whiskey, etc. It is also possible to order beer at clubs, although they may only have Heineken, which will be brought to your table in bulk, but drinking bottles of liquor is more common. Ordering single mixed drinks or wine is rare and discouraged at these places.
Nightclubs (disco, vu truong) in Vietnam can also be split into purely local, Western, and mixed.
There are many clubs in the suburbs with cheaper prices and catering exclusively to locals. In District 1 of Saigon you will find some clubs which are better for showing off and taking girls to or finding an attractive PR girl to try to take home. Some popular clubs in Saigon: 030, Gossip, Lavish.
In District 1 you will also find the few clubs in Vietnam that resemble clubs outside of Asia, such as Lush or Vasco's. Apocalypse Now (Apo) is another bar/club in downtown Saigon and it caters mostly to foreigners (a mix of tourists and expats), prostitutes, and gays, making for an interesting atmosphere.
In Vietnam, totally unlike in the West, bars and clubs are not the place to go to pick up girls, unless you are trying to pick up the staff (PR girls). Many Vietnamse men will go to Vietnamese clubs expressly to pick up PR girls. But if you are a foreigner you can meet certain Vietnamese girls who are available to foreigners at places like Apocalypse Now. They may be prostitutes.
At Vietnamese clubs, you are expected to tip graciously. Each PR girl who spends significant time at your table should get a tip, something like 100k per hour. Then you will find that the bus boys, security guards, and perhaps even the manager will come to you hoping for tips, although they don't need such big tips. Once you are outside, if you didn't take a taxi, you may find that you are forced to tip the parking attendant through illegal overcharging.
The music at most Vietnamese clubs is the same - some kind of hard Vietnamese trance completely out of touch with the electronic dance music being played elsewhere around the world. DJs here stay truly nameless. There are no famous DJs in Vietnam and when big name DJs from the US or Europe do come to Vietnamese clubs, they mostly only get patronage from the expats. Unfortunately, there is little appreciation for electronic dance music in Vietnam compared to the rest of the world, even other southeast Asian countries like Singapore, Thailand, or the Philippines.
Difference between Saigon and Hanoi
Saigon has the most clubs while Hanoi does have clubs, but like all things fun in Vietnam, the government clamps down harder on establishments in Hanoi. Places close earlier there and clubs may be a lot smaller. In Hanoi's winter, the young people go out less at night, preferring to stay in.
Outside of the two big cities, there are a handful of clubs in Da Nang (Phuong Dong, Vegas, etc.), while the smaller cities like Buon Me Thuot or Dalat can support one or so bar each. Beach resort towns like Nha Trang, Mui Ne, and Vung Tau, have clubs for both foreign and domestic tourists.
Foreigners will probably hate Vietnamese clubs and so I wouldn't recommend going to them unless you like spending obscene amounts of money on counterfeit alcoholic drinks while listening to bad "techno" music that is at tinnitus-inducing volumes in order to communicate by yelling with girls who are paid to entertain you.
Sometimes I get asked this: Are there any strip clubs in Vietnam? If you're Vietnamese, you would probably answer "no" or "what is a strip club?" In the West, we're used to there being places where girls are paid to take their clothes off and dance on stage in front of strangers. In Vietnam, girls wear tshirts and jeans in the water at the beach because they are shy.
AFAIK, there are no strip joints or nudie bars in Vietnam. Point one out if I'm wrong. I've heard rumors of a private dancer club oh Phu Quoc island which is only open to foreigners, but this could be something more like I'll explain below.
Strip clubs, even videos of what you might see inside a strip club, are illegal in Vietnam. Pornography in Vietnam is illegal and you should not try bringing girly magazines into the country. But you will still find guys peddling illegal porn on DVDs on the back of their bikes. And at least one men's magazine, belonging to a friend, has a license to show bare nipples - if done tastefully. In the movie theaters the foreign films with nudity are censored.
So where do older men go to entertain themselves and their business associates? Answer: Karaoke
But not just ordinary karaoke where you go with your friends to sing songs to a badly-rendered MIDI sondtrack. The Vietnamese call it "karaoke om" and where "xe om" literally means a vehicle you hug because you hold on to the driver, here "karaoke om" means a place where you can hug girls. But at some of these karaoke oms, you don't just get to put your arms around the girls. Some of these karaoke joints can get pretty wild with girls taking off their girls and dancing on top of tables while the patrons drink expensive alcohol. Sound familiar?
Perhaps the difference is in how public a strip club is and how private a karaoke om is. There are no signs outside of a karaoke om advertising what services it provides. No red lights or images of girls.
I'm not sure what other countries are like this. Are there strip clubs in Communist China? I think Cambodia is the same as Vietnam and I assume Laos is as well, whereas Thailand is totally the opposite.