Looking at the greater picture I would predict that the issue isn't the coffee here.
Making implicit or explicit lists of contributions in a relationship to derive what everybody is entitled to expect or demand from the other one or which expectation is rude or not usually doesn't work, at least not in a way that helps the relationship.
Everything is voluntary, even the most tiny bit you receive or give. Likewise it can be refused to be given at any time.
Let this sink in for a moment and become clear about what this means: You have a lot to be grateful for.
From that position of gratitude you will naturally feel an urge to return something. Do not let any rules or considerations or conventions dictate what you feel there, just listen to what you yourself feel intuitively. That which you feel you want to do or give purely out of gratitude is what you should do and give. No long-term obligations involved, it can change from moment to moment.
Explicit contracts ("I do this if you do that") have a time and place too, also in relationships, but the way I see it you're both far from reaching that common ground here. You're also not asking how to reach that stage, you're asking how to tell him something is rude. (Which is even a little rude in itself.)
However to answer that too: Telling someone that something is rude is just as simple as saying that it's rude from your point of view. You can also add that you're not willing to discuss on that level. And then just stop discussing about it as long as what is coming feels rude to you.
Just be warned: It may not have the effect you're expecting alone because finding a good solution in a relationship always means listening. You can't just talk and hope to be understood and having solved the issue. You need curiosity and wonder more than solutions and answers.
Your partner also has an own perception, and even if you disagree (which is not uncommon), try to see this: It can be a very fruitful act of love to respect and support someone else's opinion even if you don't share it. Don't necessarily try to cultivate this, just see if it comes to you naturally out of that position of gratitude. Not every disagreement is worth arguing about it.
If each of you is acting from a position like: "I only do this if you do yours first.", then who's to start giving? In case you're thinking: "Yeah, I'd be willing to make a start, but I'm afraid he might not return the favor.", ask yourself if you're really worried about this. If so, ask yourself if this is the relationship you want to be in. If you're not worried, then why not just do that thing which makes his day a little better and be patient to be surprised when you least expect it?
A life is long, if this relationship means anything to you, you may as well count it in years, not in days or weeks. A lot can happen there. You may have an accident next month and he has to take care of everything, including your income and visiting you every day, for weeks. You may be lying in your bed and wondering how you could ever make up for it, and you may be a little embarrassed about the coffee thing you were hesitating to make before because now you'd love to make a coffee for him. At least a situation like this might change your mind.
Seeing it in the perspective of years also makes you realize how ridiculous it can be negotiating everything in the present. At some point your love for each other must exceed all other factors, otherwise how are you ever going to reach a sustainable conclusion on anything? Think about that for a moment. Just ask yourself: How could it possibly work if there's not more love for each other than any other factor?
Just in case you're doubting that love, then wouldn't that raise other questions which are more urgent than the coffee here?
Please note that I'm NOT recommending to you to make his coffee. I'm only suggesting to consider a couple of things I think are important. The solution will develop from it naturally.
You might also discover in the process that you don't feel any gratitude from his side and that this is the thing you're really asking about here between the lines.
If that's so and it makes you angry, that's a strong sign that you lack gratitude as well, which should be addressed first then.
If however you're not angry about it and you have all gratitude for everything and yet you're not happy anymore, if you see the situation as it is and you're peaceful about it like that, you'll naturally feel the next steps to take.
Relationships always make us look in the mirror. There's no point in cleaning or even replacing the mirror if you don't like what you see there.
Ultimately all argument and conflict is with yourself, and this is where it has to be solved or dissolved.