Why do I have to tell my gender?
State Railways of Thailand has implemented lady-only cars for additional safety for the girls. Only female passengers are allowed inside these cars. Also if you book only one seat in a VIP compartment Railways will sell the other one to a person of the same gender. If you fail to provide the right information you will be refused to board. There is nothing we can do to help. End of story.
Don't try to be funny, State Railways of Thailand is very very strict on this topic.