You court inaccuracy when you apply your western standards that seem logical to you to customs in another culture. "Farang" is a common term to label a person of a western nationality. It can be used in a derogatory way or as a socially accepted label.
But I suppose if you behave like an idiot and are called a farang, the derogatory term fits
If I'm called a farang, I just smile, give thumbs up and say "farang dee"