I felt guilty for not writing Torchwood for a while... :( So, anyway. x
Owen's always been a bit of a bitch, but he's never cruel. He and Ianto remind Jack of puppies, play fighting. The snide comments and the sarcasm cheer him up. It's such a human thing.
But he knows that sometimes bitchy comments can hurt, not deliberately. And again, he knows that Owen will recognise this and look after Ianto from a distance, until he's alright again. And then he'll be extra snide to Ianto, who'll be extra sarcastic back, whether out of embarrassment or just catching up lost time, Jack can never tell.
But when Owen catches him smiling at the two of them and angrily demands why, Jack can't say that it's funny. It's funny when they fight because he knows underneath it that they really do care.
And that's just such a human thing.