Sorry, if this has been asked 100 times, I even tried the embassy, but I get an error message. With 60 day visa exempt, can I go and come back once within the 60 days? This would NOT be a 'visa run', obvioudly, but just a flight to Vietnam for 2 days, in order not to lose my 'Flying Blue' frequent flyer miles by taking a short flight on a partner airline, and crediting the miles to 'Flying Blue'. Just one clear answer is all I need, thanks in advance.
TLDR : Answer Summary
Yes, you can travel to Vietnam and return to Thailand within the 60-day visa exemption period. When you exit Thailand, you will use the visa exemption stamp you received upon your initial entry. When you return, if granted entry, you will receive a new 60-day visa exemption stamp. This is not considered a 'visa run' in the traditional sense, as you are simply making a short trip to maintain your frequent flyer miles.