I have a friend who refuses to watch any Doctor who isn't David Tennant.
While Series 6 was airing, I had forgotten that he wasn’t keeping up with the Matt Smith episodes. So I made some comment about the Silence, and he obviously had no idea what that was. Because I hadn’t realized right away that he wouldn’t know the Silence since they’re currently an Eleven-exclusive nemesis, I thought he was making a really clever joke about forgetting the Silence.
The conversation that ensued was something along the lines of…
Me: The Silence are the creepiest!
Him: The what?
Me: The Sil- oh, I, mean, what?

Him: What’s that?
Me: Huh? Did you hear something?
Him: What are the Silence?
Me: The Silence? The Silence!
Him: Yes, what are they?
Me: Wait, the what?
Him: What?

This went on for a good couple of minutes before I realized he had never seen Series 6.