Rose leans on the back of the Doctor's chair, talking about Captain Jack: "So he's vanished into thin air. Why is it always the great-looking ones who do that?" The Doctor gives her a look, and says that he's trying not to be insulted, and I mean: that's like all you do, dude. It's your whole thing. She waves a hand: "I mean men." And again he smiles sarcastically: "Okay, thanks. That really helped." In the corner, a radio comes alive, Jack's voice over the speakers: "Rose? Doctor? Can you hear me? I'm back on my ship." So he's at least capable. Generally when people give you the speech about "I'm just this" or "I'm just that," they are totally not that. Jack's not a con; he's just fucked up, and every iteration is another reason to disregard it. That's why they have to keep telling you: it's something fictional. It's a way to rewrite the information.