How did the Nazis figure out whether a person or community is 'Aryan' or not?

And then we get sexy time with them?

Ultimately, what made a group of people “Aryan” or not came down to how much they wanted them to be “Aryan”.

Nazi racism was not actually scientific, it was just a load of bullshit with a thin patina of “science-y” garwharbl to justify what was basically a totally ideological belief.

Why am I dreaming of people I've never seen before?

They used their “spidey sense”.

It was all bullshit the Nazis made up as they went along. Trying to cast it in real scientific terms is a waste of time.

If the Nazis wanted someone to be “Aryan”, they made up some cock and Bull story to justify it. If they wanted the opposite, they could be equally inventive in assigning someone to “Untermensch” status.

How can we become the best humans? How can we trust each other?

Poles are “ugly, subhuman Slavs” but hey, Hermann, have you noticed how hot and blond those leggy Polish chicks look? They don’t fit our “subhuman” model at all! İn fact, they kind of look like our Aryan ideal personified!

Ja, well, Helmut, it’s very simple. Those hot leggy blondes are actually not Slavs at all but are, in fact, Aryans who got Slavicised. We need to rescue them from the pit of subhumanism that surrounds them by immediately giving them Aryan status!

And then we get sexy time with them!

The world of the Harry Potter series is usually considered bad worldbuilding. What are some examples of actually good worldbuilding in the books/movies?