After some time spent in thailand I can't that I have seen many thai girls practise anal sex. to be honest all those I went didn't. Apparently on my first arrival, in the middle of my drunkenness I started asking for it to the girl I had picked on kao san ( according to her because I don't remember ) She told me that she was about to leave the hotel room because I had asked for that and apparently it hurt her feelings because she ain't no ladyboy. And everybody knows anal sex if a ladyboy's thing... Actually it wasn't the first time I had a react telling me to go see a ladyboy if that's my thing..
did you also notice girls being so vehemently anti anal in thailand?
( I know now that you can ask for this service at some notorious places but it seems those who don't do it will let you know in a non ambiguous way )