The many dive schools around Sairee Beach on Koh Tao, Thailand means that there are a lot of non-Thai people to be found on Koh Tao. Each diving school, and there are a lot of them, seems to be staffed almost entirely by foreigners servicing customers who are themselves almost all foreigners. Everyone from the receptionist to the dive instructors seemed to be westerners. No problems with language barriers here.
Most of the westerners to be found on Koh Tao are either being employed to teach diving or are paying to learn to dive. Now, diving is very much a day time activity. It's possible to do it at night but the prospect of being underwater, in the dark, not able to see outside of the area illuminated by your torch is understandably not very popular. That raises the question, if you're only diving during the day, then what are you going to do at night?
Another type of business has sprung up in abundance to answer that question. Bars.
Koh Tao is definitely more sedate than the likes of Koh Phangan. People going diving tomorrow morning are less likely to decide that greeting the sunrise barefoot on the beach while trying to set some sort of blood alcohol world record is a good idea. There are however a good many night time drinking options.
Every Monday, Wednesday and Friday night there are organised pub crawls starting at 5pm(ish) at Choppers Bar Sairee for around 350 baht per person. These events are advertised everywhere on Koh Tao and actually look like a lot of fun if you are young(ish) and love drinking free or cheap booze all night long.
Along with the organised drinking events, many bars on the island have nightly drink specials, like cocktails for 89 Baht each and two for one beers. The cocktails are usually fairly well made and very strong. They don't skimp on the booze like most bars do at home so be careful. Delicious yet highly alcoholic drinks can creep up on you.
Koh Tao is a fairly unique island. You can dive by day, party by night and maybe get some sleep by later night.