"Never left Britain?" Jack asks, raising an eyebrow at the other man. "Oh, lord. You're worse than Ianto, and he's Welsh," he says, emphasizing the Welsh bit. "Please tell me that you've at least been to another country aside from England. It'd be a crying shame to not at least get a little traveling done, even if it isn't that far." This coming from a man who'd traveled through space and time in a little blue box. Of course he's advocating going out to seek all the adventure that you can.

He is, of course, just taking the piss, and it's obvious to tell that for all of his shock and awe at Sebastian not having traveled, there are no negative feelings associated with the fact that perhaps the other has stayed right where he grew up. Everyone has their reasons, and Jack recognizes that.