What things about a human race we accept as "normal", but someone who is not from this planet wouldn't understand?
This post may include affiliate links.
The most intellectually advanced species on the planet is also one of the most idiotic species as well.
Good and obvious one. Members of a same species that invented spaceflight are also trying to jump in the pool from a house roof.
Where to start... Geographical borders, governments, wars, socioeconomic divides, etc., pretty much anything and everything we do to pretend we're not all human beings regardless of where we live, what we look like, what language we speak, who we form relationships with, etc., and of the same planet. I can imagine them saying "So... you all live in this beautiful planet and you are destroying each other AND the planet's natural resources along the way? Something must have gone wrong with your evolution somewhere..."
"So humans inhale toxic gases from a dried plant that you can buy at nearly every store?" "Yeah, some people do." "But do they know that it could possibly end their life prematurely?" "Yeah." "So why do they do it?" "Because it feels good and it's hard to stop." "Then why start?" "To look cool." "Unbelievable."
That we have extreme reactions to some plants (like chilly) that are hot, irritating and even sickening and we still love eating them
That we keep big predators and other dangerous animals in our home without any fear. I love my dogs but if you see the size of their teeth and their strength and think about it it’s really weird how safe I feel with them. I guess that from an alien point of view it would be like sharing your sofa with a lion.
That we haven't managed to kill off all life (ourselves included, of course) on the planet yet
That flat earthers still exist.
Maybe aliens could show them the pictures of the Earth from space, so they could see it's round? Oh, wait, we have those.