In many Vietnamese families, respect toward elders is not an abstract value — it is a set of small, visible habits. Greeting the oldest person in the room first. Standing when an elder enters. Using two hands when giving or receiving something. Serving rice or tea to elders before yourself. Waiting for elders to begin eating.
Children are often taught to khoanh tay — fold their arms across the chest — and greet each adult individually by title: "Con chào ông," "Con chào bà," "Con chào cô." At a large family gathering, that can mean a full lap around the room. Many Vietnamese-Americans remember this as the first thing they had to do at every party.
The deeper idea is that age carries accumulated experience and sacrifice, and acknowledging it out loud is a form of gratitude. Skipping a greeting is not usually read as shyness. It is read as not seeing someone.
This can feel formal to people who did not grow up with it, and it can feel like scrutiny to kids raised between cultures. It is also one of the easiest things to learn as an adult: greeting elders first, by name and title, goes a very long way.