This is going to be enormously spoiler-heavy, since there’s no way to address this without describing scenes in their entirety. So, be warned, **SPOILERS** ahead.
This will be an overview of the two post credit scenes…
The Avengers (called Avengers Assemble in some territories) post credit scene: This is the scene that follows the end of the main movie, comparable to the reveal of the Tesseract following 2011′s Thor movie. In this scene, it’s revealed that villain Thanos helped Loki invade Earth by supplying the army. Although the villains lost, Thanos seems oddly-pleased at “courting death” in battle. However, “Death” is apparently the literal name of Thanos’ love-interest. This brief preview portends the exploration of the Marvel universe in later movies. So, no, it wasn’t Hellboy or whomever people were Googling at the movie’s close, it’s another character altogether who monologues about the failure of the invasion: “[The humans] are not the cowering wretches we were promised. They stand. They are unruly and therefore cannot be ruled. To challenge them is to court death.”
The Avengers post-post credits scene: This is an addendum, left out of early international releases because it hadn’t been filmed yet. The world premiere for The Avengers was April 11, 2012. The additional post-credits scene of the team eating shawarma was shot on April 12. The scene appears to follow Iron Man’s sacrifice and near death, where he’s saved from falling to Earth by The Hulk. Upon waking from a period of unconsciousness, Robert Downey Jr.’s character tells the rest of The Avengers about a great shawarma place around the corner. Chris Evans had since cut his hair and grown a beard, which was covered with prosthetics and a wig (he covered his face with his hands to further mask this). Jeremy Renner’s character sits reading a book in the destroyed, filthy restaurant. Scarlett Johansson needs to take smaller bites. As does Chris Hemsworth. And Mark Ruffalo is trying not to giggle throughout. FYI: shawarma is an Arab dish, generally meat and chicken roasted on a spit, served in pita bread (comparable to the Turkish doner kebab).