ROSEMEAD, Calif. – It wasn’t hard to pick out Junior Dos Santos at Thursday’s UFC on FOX media workout sessions, even in a room packed full of media. After all, the 6-foot-4 Brazilian slugger does tower over most of the crowd, even without shoes. But it was another feature, Dos Santos’ beaming smile, that made it easiest to track the main-event competitor down. So when does that change? When does the grin become a grimace? Hopefully never, said the UFC heavyweight title challenger.