not actually robert downey jr

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This posts candidate proving that all the avengers are actually children is: Mark ruffalo aka the Hulk

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Although Yinsen had remained vigorous with his ablutions, Stark had let himself go. This had nothing to do with any sense of giving in to misery or despair, as might have once been the case. Instead, for Tony Stark, this was business as usual. In the normal course of his normal life, once Stark became caught up in the throes of creation, personal hygiene went out the window. It usually fell to the disembodied promptings of Jarvis, or failing that, the corporeal prodding from Pepper, to remind Stark that he should think about changing the clothes he’d been wearing for three days or maybe run a razor across the bushy growth that was accruing on his face.

After the first day or so, Yinsen had simply taken to staying the hell out of Stark’s way. He had even stopped asking Stark if he was hungry since he tended not to receive answers. Instead, every so often, he would just put out food for Stark, who would - sooner or later - eat it without looking at it or even noticing that he was doing so.

-Iron Man Movie Novelization | Gif Series

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Up next is chris pratt Aka star lord the biggest child by far in guardians of the galaxy despite baby groot being there

[Tony meets Rhodey, Steve, and Bucky in the airport]

Tony: Rhodey’s friends are so good looking! He never told me this. I think, maybe I made the wrong choice? Picked wrong soldier? 

Rhodey: [covers Tony’s mouth] He can’t speak properly on zero sleep, he-he doesn’t know what he’s saying.