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

They used their “spidey sense”.

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

And then we get sexy time with them?

What do you think of India's IT Minister Ashwini Vaishnaw comparing the Indian government's efforts to build a localised AI model to sending a mission to the moon at a fraction of the cost?

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.

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!

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.

For the First Time, Scientists Spot Water Around a Young Star Similar to Our Sun - The Daily Galaxy

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.

And then we get sexy time with them!

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!

When the sun dies, could life survive on the Jupiter ocean moon Europa? - Space