I love they all just kind of accept each of the other's quirks because they all (for the most part) know each other and have seen each other in action. And then here comes Bucky, who has been kept so apart from humanity for so long, and he just has no idea how to deal with these people. So he looks at Steve and he's like what? Because Steve is the only one he knows how to handle and trusts wholeheartedly. But he's trying, and this is why we love Bucky so much.