Being in a superhero film may net you a few million dollars, but it's also hard work. You have to keep your body in amazing shape, the hours are long and once you're done you have to spend weeks, if not months, traveling the world on press junkets while reporter after reporter asks you the same inane questions about your favorite part of your own movie.
So when you get a chance to blow off steam, you take it. This is what happened when Chris Evans (Captain America) Chris Pratt (Star Lord, Raptor guy, and maybe Indiana Jones) and late night host Jimmy Fallon decided to photo bomb a few people at the Super Bowl.
I have nothing to add to this video at all. If you have a chance to get famous, be amazingly good looking and get rich doing it, I hope you spend at least some of every day enjoying it and giving people a great memory. Also: the notorious Super Bowl bet ended with both stars promising to visit a children's hospital in costume, so that's even better.