Specialty coffee people sometimes dismiss Vietnamese coffee because it’s robusta-heavy and traditionally served very sweet. This is a mistake.
The basics
Egg coffee (ca phe trung) is the obvious tourist one and worth having once. Hanoi does it better than Ho Chi Minh City.
Iced black (ca phe da) is the everyday drink and the one worth paying attention to. Strong, slightly bitter, served over ice. Simple.
The culture
Coffee shops in Vietnam are for sitting in for a long time. Nobody is rushing you out. Order one drink, stay two hours, watch the street. This is the point.
Gear
The phin filter is worth picking up. Small, cheap, produces a very strong concentrate. Brewing with one at home is slower than a pour over but the result is distinctly different — worth having in rotation.