Those who are used to Western style cocktails and prefer to drink their alcohol in the form of cocktails should tread carefully in Vietnam. A general rule of thumb is that drinks will be worse than you expect them, regardless of the venue. Even in the States, a bar with live music, a dance floor or other entertainment expected to have worse then average drinks. But in Vietnam, even a nice hotel bar with a long cocktail menu will mess up anything more complicated than a rum and coke - and that's if they have rum in the first place, more often than not they'd only be serving whiskey or vodka.
This should be expected - in a country with a GDP per capita of under 2000 US dollars, liquor from the Western world is an expensive luxury. Those in a position to afford the liquor will be more likely to drink it straight, and have an expensive bottle to signal how wealthy they are to their friends. One of the principles involved in finding good food, taken from Tyler Cowen, is that the quality food rises or falls to meet the quality demanded by the consumers. Expecting to find good cocktails in a place where no one drinks them is akin to hoping to find good Chinese food in a community with no Chinese residents.