Lao people tend to call white and black people as "falang". In Thailand, Thai people pronounce "farang" so the word is somewhat similar.
The term falang is a Lao word that is believed to have originated from "falangset" which is how Lao people refer to the country France since they were the first Europeans to be seen in Laos, so in effect all westerners are referred to as French (falang).
If you live in Laos, you will hear the term used very often. It's like westerners referring Lao people an "Asian" in their English language, and Lao people referring westerners a "falang" in our Lao language.
So the the term falang is not an insult, by any means. The word itself isn't derogatory, and most Laotians would likely feel bad if it was perceived this way.
If you are white or black and you are automatically labelled as a falang in Laos, now you understand and you shouldn't get offended at all.