According to The Bangkok US Embassy web site it says this:
U.S. citizens carrying a tourist passport and in possession of an onward or return airline ticket do not require a visa to enter Thailand.
Now, what if the return ticket is from another country (like Malaysia)?
So, if I were to take a train to Kuala Lumpur, would I need to obtain a visa? Or, will they not care because I'm leaving the country and I at least have a return ticket.
The total trip will only be 7 days.