If an alien civilization were to visit Earth, what movie would you pick to show them in order to give them a summary of what mankind is all about?

Schindler's List. Humans can be nasty, horrible, utterly evil. It's all too common. But some of us will work to do good. Some of us will push back and do what's right. There is evil in this world, but there is also goodness.
- "Contact" for a similar reason. It's a mix of all motivations, along with people's general mistrust of each other.
- Samsara for the same reason. It shows beauty mixed with terrifying images of human impact.

300
Let them think humanity is 99% buff oily badasses in speedos who will gladly fuck you up until their dying breath.

My autistic ass would have them watch all three Lord of the Rings movies. Y'all need to find a better diplomat than me.
- My first thought too 😅

Don't Look Up - https://www.rottentomatoes.com/m/dont_look_up_2021
Sort of summarizes the total shit-show that current politicians and billionaires are responsible for.

Mean girls
- On a Wednesday and make everyone wear pink, so the aliens feel ashamed for not wearing pink.

Idiocracy.
Real answer though, 2001 a space odyssey.
- Idiocracy was honestly my first thought, but they wouldn't have all the cultural nuance required to understand it. Someone else said Don't Look Up, which I think would get through the irrationality a bit better.
- Haha 2001 was my first thought, and Idiocracy was my second.

Independence Day.
I'll tell them it was a documentary. Or at least based on a true story.
- "Interesting! Tell us, where are these aliens with terrible cybersecurity? We were thinking of conquering you, but now it's pretty clear that there's an easier and wealthier target."

Just the entire Cunk on Earth series.
100% factual information about human history.

Don't Look Up
- The depressing thing about that movie is that in some ways it was exaggerated like satire usually is, but in others they actually toned down the stupidity.
  
  The premise is exaggerated, but the actions are clearly better than were handling things in real life.

Orgasmo. The '97 one, not the '69 one. ... fuck it, also the '69 one. Make it a double-feature.

You should show them my latest movie that I can't promote right now.
They would be so confused, it would be hilarious.

Life in a Day
Not a movie exactly, creators asked some basic questions and invited people to submit footage from a single day in July 2010. Exciting or mundane, anything.
It’s really well put together and always gives me a refreshed perspective on my place in the world.
They did it again in 2020, during the pandemic.
- A Serbian Film

Baraka... but they'd be 30 years out of sync with today :-)
- I feel like it stood the test of time. Was my top pick with Idiocracy being a close second.
- Why not Samsara?

Obviously the complete Stargate franchise. Humans don't put up with aliens tryin' to pull any shit.

Obviously the greatest documentary ever committed to film: The Adventures of Buckaroo Banzai Across the 8th Dimension.

Double Feature: Ender's Game (2013) and Starship Troopers (1997) - then we serve them a sumptuous shellfish tower to discuss their surrender over dinner.
- I thought the movie did a decent job of telling the story considering the limitations of the medium.
  According to the author many studios have approached him over the years with unacceptable alterations and that one was the first one to come along with anything good enough.
  He said it had to be literally children, first of all, and they always wanted to change that.
- Yeah, let them read the book and tell them that sadly no movie has ever been made.

Letting them know what mankind is all about seems like a terrible idea. We're jerks.

The Day the Earth Stood Still (1951) - Literally telling aliens that we will fuck shit up.
Stalker (1979) - You can leave your garbage and we'll think it's treasure.
Dude, Where's My Car? (2000) - Humanity is really just a bunch of idiots, stumbling through everything.