"Mafia? Sounds like a fun game!"
Gokudera's yelling at him again, saying that the Mafia is not a game. Yamamoto rubs the back of his neck as he tries to calm his classmate down, reassuring him that he thought that the Mafia was a very serious game. Not just any game, but one that sounded like a lot of fun.
Life was a stage and the Mafia was just another scene change for him.
Yamamoto's been playing at this charade for as long as he can remember, ever since he squeezed Mother's hand, too young to understand why her grip was so weak, ever since his father came stumbling home one day with tears and snot running down his face (he can't forget the strong smell of sake that clung to his father's clothes that night).
He claps Gokudera on the shoulder, tells him that he's going to pop a vein if he doesn't settle down, which only seems to make the "right hand man" angrier (maybe it's code name for pitcher, someone really important to the game that Tsuna's been thrust into).
Life is but a baseball diamond to him (you never know when you'll strike out).