One of the first things Robert said when we were meeting about the movie was “There’s no way Tony Stark gets in a room with Bruce Banner and doesn’t poke him”. There’s no way. He wants to see it happen, he wants to see how that guy works. And that is not only true, not only ended up in the movie but ultimately informs their entire arc, which is one of my favourite things in the movie. The idea that Tony Stark is not intimidated by the concept of the Hulk and, in fact, thinks that Bruce needs to embrace his inner Hulk as it were, sounds like pure classic Tony irresponsibility and in fact it is you know what saves us all and ultimately what saves Tony because he allows Bruce to…he sets him up and lets him gets to the place where he can decide to be the Hulk.
Joss Whedon on the Tony/Bruce relationship (The Avengers Blu Ray Commentary)
I love how well RDJ knows Tony, he’s like, “This has to happen” and it does.