I just put it down to them being thick, they should know many farang have been here years,
The only time I did get offended was Nakorn Si Thammerat were i was to told to <deleted> off out of Thailand in Thai obviously,
I used to like go in a bar and sit there listening to the gossip I cant do it where I live to many people know me or the wife, One of them will warn the others, be careful he speaks Thai or I have a Thai wife,
Another time in a restaurant I use, and on the next table 4 of them were bang at it about how dangerous it was farangs speaking Thai, until I paid my bill and walked past them and spoke Thai to them, Idiots