When you come at these things from a different direction it can be surprisingly easy to miss some blatant stuff.

Yeah, I think it would be unfair to expect Czech developer to be familiar with EVERY form of American racism when there's so many to choose from.

Even when you're in the culture where it's prevalent, if you're not looking for it you don't see it. A decent number of folks have emails ending in 88 or 1488. My high school had to repaint part of a mural because the guy on it was making a white supremacy symbol (apparently middle and index fingers together to make a W, this was back in the 90s and I haven't heard of it since). When the world is full of hateful dogwhistles, sometimes people are just whistling.

That said, it's about what happens after it's pointed out. Altogether too many people double down, and the innocent mistake starts to look a lot less innocent.

I hadn't ever heard of the 88 thing! Had to google it. And I'm not exactly socially oblivious, at times I've been accused of being preachy! Just not - you know - familiar with the intricacies of that particular form of racism. So I guess... Case in point

Yeah, that one's always been around, but has become more prevalent in the last few years as the supremacists have become less subtle.