what a dick you are, he is leaving Thailand to go to Sri Lanka, how else would he be getting there If not departing by an international airport, on a boar? Taxi? Walking??
Pfft as for your newbie comment, hardly think living In Thailand for 13 years puts me in that box, so get back in yours pal
BS you're telling me the IO's at the "international airport in Bangkok " work independently AND DONT SPEAK ENGLISH, give your head a shake feller, or maybe leave off the bong till night time
Type "visa agent's in samui, Thailand" into that thing called Google or Google maps and hey-presto you will magically get a list of many, with locations and phone numbers
cos if you read my comment properly you will understand my frustration this question is asked 5 times daily, maybe stupid people shouldn't venture around the world if the don't know the rules and regulations on the country they are entering
You need to do more research, if you did it properly you will see that you will get a visa except stamp on arrival NOT A VISA
Or just "search" your question in this group as it's asked 4 or 5 times per day by fools who don't have a clue about the how's and why's of entering Thailand