I understand that people are sensitive to different things at different levels. So that this is a sore spot for you I get, and fair enough. I thought you knew me well enough to know that I don't take that kind of stereotyping seriously, and that I'm about as far from nationalistic as one can get. But again, I get that we all have stuff that gets under our skin, and I'm not saying you're wrong for not being amused even if my intentions weren't malevolent.
Where you lose any semblance of moral high ground, though, is how you've handled it. You're assuming my motivations while also overgeneralizing about a country, at the same time that you're complaining about overgeneralizations. If you'd just said "hey, this is a sore spot for me, don't joke about it," I would've respected that. That's the grown-up way to deal with a difference in interpretations and/or sensitivities. But I don't respect a temper tantrum or a baseless assumption of bad faith.