They were all laughing and joking and making fun of the big bro and the prank they pulled on him, which caused him to fall into the shark infested waters. I mean, yeah, they thought they took out the big shark, but it wasn't more than a few minutes earlier that they showed how the waters was full of smaller sharks. The only thing missing from that scene was a shark going after the poor fellow as the rather typecast black funnyman films it in his cellphone and yells "WORLDSTAR!!!!!".