Robert Downey Jr.’s delivery of his “Genius, billionaire, playboy philanthropist” line in The Avengers changes between the trailer and the film.
This is the line from the trailer:
I like this reading. The slight stumble and pause for thought gives it an improvised tone which undercuts the arrogance of it. The impression here is that Stark has never thought about this before but his quick wit provides him a with great response that’s hard to argue with.
Here’s the same line from the film. Captain America’s feed line has changed as well but only slightly:
I hate this reading. It’s delivered without hesitation or thought as if Stark has prepared it in advance for just such an occasion; coupled with the look he gives in return, it’s unbearably smug. It adds to the tension of the scene because even though he’s correct, you’re left wanting to smack him in the mouth. Yeah, you’re all those things, but…fuck you!
Which is the point. The reading of the line in the trailer is great for a trailer — it’s funny and memorable — but in the context of the scene, where everyone’s at each other’s throat, it doesn’t work. The alternative reading of the line isn’t going to break the tension with humour but instead will ramp up the tension even more, with even calm, reasonable Steve Rogers left demanding that Stark put his suit on just so he can beat the crap out of him. It’s Stark at his worst, it’s Rogers at his worst and it winds up everyone in the room even more until the simple beeping of scientific equipment snaps everyone out of it.