Tony was trying not to laugh because obviously the big guy was upset, and him laughing would make it worse. He also knew it was a nervous tick of his, and if he laughed it wouldn't be done out of sheer amusement. That was why he ducked his head down a little bit and tried to stifle a snerk with his face scrunched up.
Sulky Hulk was kind of cool, actually. He did miss Bruce though, and he did want Bruce back. He coughed to clear his throat, like that would cover up the stifling, and was able to keep a straight face again.
"Hey, I like Bruce. He's my friend. But there's no reason you and I can't be friends, too. I'm here to help you too, ok? So whatever you want....pizza, violent cartoons, Angry Girl? I'll make sure you get it."