The funniest thing in this scene isn't so much the drama on the Avengers end as it is the lack of drama of Rhodey's end. He's delivering earth('s-mightiest-heroes)-shattering news and he's treating it like he can't come over to play after school today. He's just so...deadpan.
I mean, imagine this same conversation taking place under different circumstances! Rhodey: "Oh sorry guys I kind of let Ultron out, btw" Janey: "Ultron's free?!" Cap: *snatches phone* "Iron Man, this is Cap! What do you mean Ultron's free?!" Rhodey: "Yeah I thought he needed a walk, but I forgot his leash. I'm sure he'll come back home or something" Thor: "Wait, what the hell, man?!" *click*