Jock (insult)

Jock was a mild insult meaning "someone from Scotland". Jacko once derisively called Jamie McCrimmon "Jock" in Atlantis, and the Scotsman instantly bristled. He swiftly informed Jacko that his name was not Jock but Jamie. (TV: The Underwater Menace)

Behind the scenes
Though "Jock" is undefined in the episode, the contextual meaning is clear.