On your left
One of the most fun things about watching all of the movies in the Marvel Cinematic Universe is seeing in-jokes crop up over again. The characters themselves often like referencing things from previous films, and it makes observant viewers feel in the know when they notice this banter as well.
The phrase “on your left” is one of the more famous examples of these. First heard in Captain America: The Winter Soldier at Falcon and Captain America’s first meeting, Cap gets a text just before the time portals open up at the end of Avengers: Endgame saying “On your left,” to let him know that Falcon has returned. It’s quite the victorious moment.