The reason that Xander has the xXx tattoo is, as Gibbons says "You have three X's tattooed on the back of your neck. I think that's rather appropriate, since you're looking at three strikes. Grand theft auto, reckless endangerment, and that little bridge stunt of yours makes you a three-time loser. Maybe you ought to call yourself "Triple X." But if you do what I want, I'll make all your little recent criminal transgressions go away and let you get back to that pathetic excuse of a life." It is that moment that he offers Xander to join his spy cell. It is only because of Xander that it is called "The Triple X Program" and when Darius Stone is chosen it is because he is of a similar mentality(He is serving time in Jail, 9 years of a 20 year sentance and is a former Navy Seal...A perfect candidate.). Edit: Also every lead agent of The Triple X Program has a specialty. Xander's just so happens to be extreme sports, Darius' is hijacking and souping up cars/tanks and diving(He's a navy seal after all) and Neymar's is Soccer. Double Edit: Just got to the end of the episode and they go over the Tattoo.