Lieutenant Oblivious
The person (typically in online discussions) that is somehow ignorant of a very popular meme, reference, or trend, and needs explanation in order to properly understand it. A subordinate and a counterpart of sorts to Captain Obvious.
Larry (upon seeing something beyond his comprehension): "I don't get it."
Lemmy: "Captain Obvious, come in: this is Lieutenant Oblivious requesting backup, over."
Lemmy: "Captain Obvious, come in: this is Lieutenant Oblivious requesting backup, over."