Thai people are very friendly and earned their country the name “Land of the smiles” for good reason. They are also very conservative (although it may not seem like it in parts of Bangkok). It is your responsibility as a traveler to do your best at following local customs and keeping the locals from becoming jaded toward future visitors. Don’t screw it up for the rest of us!
Locals understand that you may not know the customs and they are extremely patient. If you at least try then is shows that you are not just there to use them as servants for your holiday trip. Long after you have partied yourself stupid and left for another country, they still remain behind and have to scrape out a living. It is easy to see why some of them become jaded and want to throw your Singah at you.
Abiding by the local customs is not only personally enriching, but it can help you get better services, prices, and treatment everywhere that you go. By simply removing your shoes a shopkeeper may give you a fairer price.