Thirteen years old is a tough age and maybe the boy hasn’t been taught the best manners. When I was 13 I certainly wouldn’t have thought to thank someone who took me somewhere. I would have thought that the fact that I went with them showed I liked it and that was enough. I think at some point in time he will remember that you did nice things for him, but I wouldn’t count on it happening any time soon.
One of the reasons 13 years old can be a tough age is that sometimes when 13 year olds feel as if their opinions are totally ignored they don’t know how to cope with it in a constructive manner. They haven’t learned how to self-advocate in a way that is both polite and firm. Sometimes, their parents give them no options that are both polite and firm. It is either “do what I say” or nothing. That is tough when you have started to gain an appropriate sense of independence and know that there is a degree to which it is OK when what you want and your parents think you “ought to” want are two very different things. They can make you do what they want, but it is understandable that a 13 year old might find a way to say, “this is what THEY want, not what I want, so let’s have no confusion on that point.” Putting an outside adult into the middle of that
with no warning is not a nice thing to do, whether that adult is lending tutoring, coaching, a ride, or just supervision. (The worst is leading the adult to believe the child* wants* to be a helper for some group project when in fact the parent wants the adult as a supervisor/babysitter/warden for their out-of-control child, but that is a rant I will leave for elsewhere.)
I would actually be concerned that the young man was a puke because this trip was not his idea and he felt insulted because he was being “foisted off” on a young relative. The young fellow had birthday money to spend. Maybe he resented that neither his parents nor grandparents nor anyone else he craved some time with was willing to part with the one-on-one time with him to enjoy his birthday treat with him. He could have felt that his birthday was seen as too much of an imposition on his parents to be spent with him, and punished his older cousin for it for the “sin” of being complicit with their “neglect.”
I would actually ask him about that. I’d say, “were you mad at me when we went out on your birthday?” If he said no, I could say, “well, you were swearing all the time and never thanked me, so I thought maybe there was more to the story than I knew. It was supposed to be a good time for you, the day you got a treat to celebrate your birthday. Usually when you enjoy your time with someone, you don’t swear at them and you naturally say, ‘thank you, I hope we can do this again some time’ when you’re done. I don’t want to be the manners police; I just want to make sure there wasn’t something about that whole set-up that I didn’t know about. I care about whether you are nice to me, but I also care about whether or not you had a good time to celebrate your birthday. Do you see what I mean?”
If he said, “yes,” then I’d tell him I’d rather he be direct and tell me what was bothering him rather than just being generally abusive, because I can’t do anything to make a situation better when I don’t know what is wrong in the first place. For instance, we could have gone back to his parents place and not spent his money doing something he didn’t want to do.
He might come away looking at the situation differently or he might not, but he might realize that he was punishing someone else who could have maybe helped for something that he or she did not cause. He might realize that the cousin actually would take his side if he didn’t like the way his birthday treat was working out. He didn’t have to resign himself to a waste of money or spend the whole time brooding over the waste or take his frustration out on an innocent party.
Oh, and by the way, do talk to him as if he were a young man who rightly has opinions of his own, whether or not they are realistic, and not automatically a rebellious little kid who deserves no sympathy at all whenever he doesn’t agree with his parents. Respect of that kind is not wasted on the young.