It is true that the word “farang” (ฝรั่ง) derives from the word “Franco” (but with Thai pronunciation) and is often applied to all Caucasians (and even Black Africans – black farang?). Today the meaning has shifted to encapsulate all non-Asian foreigners. Whether there is any offence involved should be a matter of how the word is used and in what context.

The Francos where one the first “white” people for Thais to come across (the other being Portuguese) and this was the simple way Thais used to identify such people (as Caucasians). There is certainly a race element to the word meaning but to call the word itself as racist (i.e. offensive) is stretching it.

For Thais who have been swept up in this neo-liberal group-think they might use the word “khon tung prateet/chart” (คนต่างประเทศ/ชาติ) instead but it is rarely used and more typically used in formal settings.

Farang is universally used outside hi-so Bangkok.

It does not mean Foreigner. It is a derogate word to describe the French (Franco) during the Paknam incident of 1893. I suggest you check your history.