It is an extremely arrogant attitude to live in another country and pretend that the local people speak your language. To be honest, if I was thai I'd easily send you all to hell, especially those of you who get mad at me for not understanding your slang.
That being said, it's a very difficult language to learn, but this is no excuse, if you're living here you should at least show to locals a little bit of interest in learning and speaking their language. Otherwise you are just a colonialist.