Captain Jack Harkness was a charmer; that was the first thing the Doctor noticed about him. With his white teeth flashing in a blinding, perfect smile and a few well-chosen words he could have practically anyone eating out of his hand. Man, woman, alien, it didn’t matter; the Captain was indiscriminate.
Rose fell under his spell immediately, lapping up the dashing Captain’s attention, something the Doctor couldn’t help noticing. It was annoying. Could he be jealous? Surely not; he had no reason to be.
Nevertheless, if he were honest with himself, even he wasn’t completely immune to Jack’s effortless charm.