Akagi's (almost) unflappable-ness is because he's aware of his status as the main character in a Prequel.
As is mentioned repeatedly in the series, any normal person would fear death, even subconsciously, or become an obsessive Death Seeker
and sabotage his own chances to live, to the point of being Driven to Suicide
But Akagi isn't a normal person. He knows he has Plot Armor
—not just of the normal protagonist kind, but the extra strength of the knowledge that he appears in Ten
alive and well. He is indeed a genius player of the highest caliber, but he is willing and able to take the seemingly insane risks he does because he's seen all the way past the Fourth Wall and keeps himself entertained by watching how the events unfold before him. His laughter, then, isn't so much aimed at his opponents, but rather at the author, as if silently challenging him: "Well? How do you plan on getting me out of this