This is something I’ve gotten a lot better at, but there’s plenty of room for improvement. It is an inherent trait with many westerners, and something we all should work very hard at curbing.
When a boy does something you perceive was wrong, even a waiter in a restaurant or bar, just tell him one time. Be direct and to the point, but careful to avoid suggesting he was bad or stupid. Then drop it!
The fact that he does not respond in a way that satisfies your needs most likely has nothing to do with his failure to understand your concern or complaint. To continue harping on it will only cause you to loose self respect (face), in the eyes of the boy, and others observing. NOT a good thing! Perhaps he knows you are wrong, but the polite thing to do is say nothing.  Maybe he was wrong, but if you voiced your concern correctly no response from him is required. And if you did not voice your concern properly, the boy probably doesn’t know how to respond. Even if a response is within him, he may not have the English skills to articulate it, so nothing said is better. Do not expect any form of apology from the boy, as this is not customary behavior. Again, if voiced correctly, no apology is necessary and you should not be looking for one.
One evening a boy was pouring my drinks too heavy, something a lot of the waiters do. I had told him in the past to not do this, but once again he had forgotten or ignored my previous requests. So I said to him, “OH! I think you want me mao (drunk) so fast. If I get mao too much maybe I can not have sex tonight.” I followed this with a big smile. He smiled back and poured my drinks correctly for the remainder of the evening. I could have gone off on him about how many times I’ve asked in the past he not pour heavy, but for what? In the eyes of Thais, it would only have made me look like an ass.
On one occasion I asked a boy working in Banana Bar to go and get me some pork balls. He came back with fish balls. I hate fish balls. So I asked why he did not get me pork balls. He said, “Finish.” I said with a smile, “OH!..thank you.” To him, or any Thai, eating is more important, so to come back empty handed would have been “more bad”. The vendor was out of pork balls, so he got me fish balls instead. Thais love fish balls, so no harm done, in his mind. To have criticized him for this would have been inappropriate. Besides, it wasn’t lost on him I only ate a few of the fish balls. Actions speak louder than words sometimes, and no one gets insulted. Later he brought me some grilled chicken, paid for out of his own pocket.
At one time there was a boy hanging out with me that worked in an office job, but didn’t make a lot of money. Even so, he had a soft heart and would give money to anyone he felt was in need. I started noticing one of the door men in Soi Twilight was hitting him up for 100 baht every time we went drinking together. So one night, when I was alone, the door man sat next to me for a visit. I said to him, “My friend not make good money and it always finish long time before he get more.” Then I said, “My friend have good heart and like to help people that need money, but he really not have money to give.” Then I looked him straight in the eye and asked, “Do you understand what I say to you?” The boy said yes, and I never brought it up again. I was also careful to have the talk with him when no one else could overhear it. And you will notice I did not accuse the door man of doing any wrong. He never asked my friend for money again.
If you don’t get an immediate answer to the situation, just file it away, and let it go. Chances are you will discover why things happened the way they did sometime down the road a bit. As with the pork balls example, what one perceives to be wrong may actually be right, if you have benefit of the Thai cultural big picture. Don’t be so quick to assume things. And right or wrong, harping on it only makes you look bad. In our culture it’s a way to find closure. In Thai culture it is exceptionally rude and disrespectful.