This is a poorly phrased question with many ambiguities that pivot around a kind of Eurocentrism. First, who defines ‘exotic’? Are you asking what Vietnamese people see as exotic? Well, the food of the Central Highlands might be considered exotic to people from Saigon. And the food of the coastal regions might be exotic to somebody along the Mekong River Delta, where catfish is consumed.
Are you asking what would be ‘exotic’ to Westerners? Because the thing is this: Things listed by another respondent—things like balut eggs—are commonly eaten all the time and a complete treat for people who think of it as part of the mainstream culinary repertoire.
I’m not going to assume that their is some kind of untoward racist intent in your question. I’ll try to give you the benefit of the doubt. But I think what you’re trying to ferret out is the ‘ick’ factor: roaches, mice, dog, etcetera.
Well, here is something for you to chew on: The most exotic food I ever ate growing up was the cafeteria food in my school in Los Angeles. All that mashed potatoes and corn dogs and diced turkey and pizzas. It was super exotic. It was like having take-away every day. And I always wondered why we didn’t get to eat jello every day at home.