Warning: MASSIVE spoilers ahead for Avengers: Infinity War! Don't read any further if you don't want to know what happens in the latest MCU blockbuster!
Few actors have ever embodied the personality of their respective characters quite like Robert Downey Jr. and his take on Tony Stark. The Iron Man star is known for his eccentric, charismatic, and downright charming persona, and it sounds like he imbued Stark with all of those qualities in Avengers: Infinity War -- even including some moments that weren't in the script. In fact, it turns out that the actor even ad-libbed one of his best lines on Ebony Maw's ship, when Stark shuts down Peter Parker (Tom Holland) following their rescue of Doctor Strange (Benedict Cumberbatch).
The scene in question occurs roughly around the halfway point of Avengers: Infinity War. When Doctor Strange, Peter Parker, and Tony Stark are regrouping after their battle with Ebony Maw, Peter proclaims that he's "backup," and Tony quickly retorts by stating that the "adults are talking." It's a fantastic moment of comic relief, and perfectly in line with Tony's character, but according to remarks made by Tom Holland during a fan Q&A at The Brothers Trust charity event (via Webbed Media), the line wasn't in the script, and it was all Downey.
This scene stands out as one of several instances of improv from the set of Avengers: Infinity War that made it into the final cut of the movie. In fact, while Robert Downey Jr. was responsible for that jab at Spider-Man, Tom Holland similarly got a moment to shine during production, as well. Later in the film when Spidey begins to fade away, his tearful pleas of "I don't want to go," were reportedly made up by Holland. Marvel Studios hones these films down to a science, but it's reasonably clear that directors Joe and Anthony Russo don't mind playing around and letting the actors explore the scenes to find some moments of improv, regardless of whether the lines are incredibly funny or incredibly dark.
Now we're left wondering how much Tony Stark will be able to quip and joke around next year when Avengers 4 debuts. Infinity War ends on a decidedly down note, with Tony watching as Doctor Strange, Peter Parker, and most of the Guardians of the Galaxy fade away before his very eyes after Thanos (Josh Brolin) snaps his fingers and unleashes the full power of the Infinity Stones. With the third Avengers movie ending on a devastating defeat the likes of which we have never seen in the Marvel Cinematic Universe, we will have to wait and see how charming and quirky Tony can become when the surviving troops rally together.