Well, yeah--sure. I do think there are people who are just bright and cheerful no matter what bombs are going off around them. What their motivation exactly is, I am not sure.

I am from rural Texas and lived in Nashville for a very long time and there is certainly a cultural component to excessive cheerfulness in parts of those states--no doubt about it. You just don't find that in NYC, say, where I also lived. I also basically lived in Australia for a bit in the early 2000s and I believe Aussies are a bit like American Texans or Southerners in the same regard. They just unbelievably gregarious and friendly and it sometimes freaks people out who are not used to it. Such a your average Brit.

I try not to let it ruin my day if someone else is ridiculously gleeful. That's their deal. Maybe not taking it as a sort of personal thing and just recognizing that some people are for whatever reason super duper cheerful, even when it is not called for, maybe just acknowledging that everybody's different and some folks just act this way will help you better let it slide off your back. We're all different.