Those of us who understand differences in languages are not likely to laugh when we hear these sounds. We might if the mood calls for it, but generally, we don't because we know that languages are going to sound different. The ones who are learning a new language or who have never learned to speak another language might.

I teach Mandarin at a high school, and my students laugh all the time whenever they hear something that sounds like something else in English or Spanish. Early on, I use this to help them remember what I'm trying to teach them, but once it becomes excessive, I start to discourage them from constantly saying "that sounds like...," because what they end up doing is only pronouncing the new words in what it "sounds like" instead of how it should be accurately pronounced.

Dung sounds like "dun" in english. That refers to "excrement" or "feces".

That is why it is funny to english speakers when we hear the name. 

But the vietnamese name has a "g" at the end, so it has a bit of a different

sound. The "ng" adds a ring to the end of the word´s pronounciation, so it

is pronounced slightly different than "dun". But it is still very closely related

in sound, thus the "funny side" to the name.

The same happens with other names, as "Phuc", "Bich", and so on.

Of course, everyone should be resepectful towards others and never use 

the differences in culture and idioms to bully or make fun of others. It is

common human decency to treat everyone with respect.

The D in Vietnamese is pronounced closer to the Z in English, whereas the Ð is equivalent to the English D.  

In fact, many Dung in America change the name slightly to Dzung even though the Z does not exist in the Vietnamese language. Some also borrow the Chinese Yung.

@Keilah - It's "dung" with a 'g' that refers to excrement.

Why would the person called 'Dung' not just choose another name?