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

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.

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.

What were the career paths of each member of "The Monkees" after the band disbanded? Did any of them have successful music careers?

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!

And then we get sexy time with them!

They used their “spidey sense”.

What to know about nerve pain and tingling hands and feet - The Washington Post

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.

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?

NASA Pulls the Plug on Europa Lander, but Scientists Propose a Plan B - Gizmodo