I have been called a farang, barang, gaijun, laowei and probably a few others (I was always struck there does not seem to be any catch-all informal phrase for Westerners in Vietnam). I find these terms are used far more often in a descriptive than an evaluative way. I have used them myself often enough. But of course they can, like any word used to classify people, be used as an insult.
It is probably a good idea to acknowledge the differences in acceptable behaviors coming from a more racially heterogeneous country where race and nationality are considered separate and a more racially homogeneous country where race and nationality are intertwined.
I remember one time I was in China (in a fairly small city without many foreigners) at a zoo. There was a little girl who was pointing at the animals and calling out their names (In Chinese of course). She would point and say, tiger, bird, monkey, and then pointed at me and yelled LAOWEI. Her mother tried to apologize, but instead we had a good laugh about it. Take your kids to the zoo and see all kinds of exotic animals, lions, tigers, monkeys and white people!
Maybe I should be more judgmental of the local cultures where I live, work and travel and be offended more often, but I am not sure how that would make my life here in Asia more profitable or enjoyable.