Ok, fun story that happened to us during our stay in Singapore. We had been warned, when in Indonesia, to be careful about places giving Thai massages as they sometimes give a little more even though the place seems legit (especially in China).
We went one day in Malaysia with our Singaporean friends and ate in Johor Baru. After the meal, Jason proposes a quick massage, and knows a good place for it where he had already been with his girlfriend. We end up going to the place, and Manny and I take a 1 hour Thai massage. It's a serious place, it is recommended by Jason and a sign is even written in the massage cabin explaining no sex deals are to be proposed. In short: "There's no danger what so ever"!
Now the fun starts when it is actually the masseuse, in the middle of the massage, that offers to "do something" pointing out your sex. Now, our first reaction was to be shocked, as we didn't expect it from a place that pretended to be serious. We both refused (we talked about it later, we weren't in the same "room"), and the masseuse then left us for a good 5 minutes.
We were puzzled by what would have happened if we had accepted, and why they actually left us alone for a while after that. Thanks to beautiful internet, we got our answers.
What they actually propose is a handjob, described by someone on reddit as a "worship to his cock". He gives a sweet and detailed description of what happened to him, but to sum it all up: "super high quality handjob. The work of a professional..."
Now this doesn't answer why they left us after for a few minutes. Internet comes again to the rescue as someone having had the same experience explains that his masseuse came back asking: "are you finished yet"! So yep, you got it, if you don't accept their service, they give you time to do it yourself :'-).