The Marvel Cinematic Universe has a whole, well, universe of details and lore to create incredible stories from. It's also got a lot of material for inside jokes and running gags. From the deep cuts to the easter eggs and everything in between, these are the subtlest of jokes in MCU movies.
1. In Guardians of the Galaxy films, there is a disclaimer in the closing credits that states: "No raccoons or tree creatures were harmed during the making of this feature. The same cannot be said for handler's of said raccoons and tree creatures."
2. In Guardians of the Galaxy, Peter Quill's ship is a nod to 80s star Alyssa Milano. As a child of the 80s, Star Lord had a big crush on the movie star, so much so that he named his ship The Milano. Alyssa Milano has said the ship being named after her is one of the cooler things that has happened in her life.
3. When Pepper Potts discovers that Obidiah Stane is selling weapons on the black market, she comes across a shipping manifest for the vessel MSC Lebowski. Jeff Bridges played both Obidiah Stane and The Dude from The Big Lebowski.
4. Red Guardian has "Karl Marx" tattoed on his knuckles in Black Widow.
5. In Shang-Chi and The Legend of The Ten Rings, Jon Jon tells Katie that he speaks "ABC." Many assumed this simply meant English, but Simu Liu explained that it means "American Born Chinese." Jon Jon saying that he speaks ABC was a nice subtle reference for audience members who immediately understood the acronym!
6. In the comics, Odin sends Thor to Earth as a humble young student named Donald Blake. Even though he never winds up as Donald Blake in the movies, there are several references to Blake.
7. One of the most memorable parts of Thor: Ragnarok was Matt Damon's cameo as "Loki." Damon has actually played Loki before in the Kevin Smith movie Dogma.
8. In The Avengers, Tony calls Thor "Point Break." In Thor: Ragnarok, Thor is unable to access Tony's ship through voice command. After trying "Thor," "Thor, Son of Odin," and "The Strongest Avenger," he finally succeeds by saying "Point Break."
9. Taika Waititi had a lot of fun with the rock jokes for Korg in Thor: Ragnarok. There's even a subtle game of rock paper scissors. Korg fails at starting a revolution because he didn't print enough pamphlets (paper beats rock). Later, he accidentally crushes Miek, who's basically a walking pair of scissors (rock beats scissors).
10. Early in Captain America: The First Avenger, Howard Stark tells Steve that Hydra "won’t attack you with pocket knives." Well, at the end of the movie a Hydra agent attacks Captain America with a pocket knife.
11. Bruce Banner (the Hulk) and Natasha Romanoff were exploring what might have turned into a lovely romance around the time of Age of Ultron. At one point in the movie, Stark asks for Romanoff's location. When she doesn't reply, he says "you and Banner better not be playing 'hide the zucchini.'" I'll just leave that there.
12. While Bruce Banner is fighting to keep himself from transforming into the Hulk in The Avengers, he stumbles on a platform that says "Warning: Contents Under Pressure."
13. Laurence Fishburne starred in both The Matrix and Ant Man and The Wasp. In a classroom scene, there are several complex formulas behind Fishburne. Any one of these mathematical problems could be a subtle nod to — oh someone literally just wrote "Matrix" on the board.
14. At one point in Ant-Man, Scott lands on the roof of a cab driver's car. The driver looks up, and the actor playing him is none other than Garret Morris, who played Ant-Man in a 1979 SNL skit. Morris was actually the first actor to ever play Ant-Man on the screen, so it's only fitting he had a cameo in the 2015 film.
15. The Avengers, Guardians of the Galaxy, Avengers: Endgame, and WandaVision have referenced the iconic Pixar easter egg "A113." This is a classroom used by graphic design and character animation students at the California Institute of the Arts.
16. Kevin Feige is a big Star Wars fan. He figured that if Phase Two of the MCU was going to be their Empire Strikes Back, they may as well have a character loose their hand, just like Luke did. Or maybe someone could lose their arm/hand in every Phase Two movie.
17. The Russo brothers started their careers directing television. One of the shows they got their start with was Arrested Development, and they included the Bluth family's stair car in Captain America: Civil War.
18. The Russo brothers have directed quite a few episodes of the show Community. In fact, it was one of the paintball episodes of the show that got Kevin Fiege interested in the Russo brothers. As a result, a few Community actors have made appearances in the Russos' movies.
19. Nodding to their Arrested Development roots, the Russo brothers included the never-nude himself, Tobias Funke, in Infinity War. Not only did they give his character a cameo, but they dressed him in his best look: covered in blue paint and wearing only jean shorts.
