In a parody of How the Grinch Stole Christmas!, all the Nicktoon characters in the city of Toonville like Nickmas a lot, with the major exception of Angelica, or "Grinchelica" as the narration refers to her. The narrator reasons that her hatred for Nickmas might be because her pigtails are tied too tight or because she can't find her Cynthia doll one night, but apparently the actual reason is because she believes she should have all the chocolate candy to herself.
Grinchelica rides into Toonville on her Malibu Cynthia sleigh, pulled by her cat Fluffy, and sneaks into the houses to steal all the chocolate goodies. Among them, she steals chocolate figures of Ultralord, Phil and Lil's chocolate worms, Rudy's chocolate chalk, and Zim's chocolate candy cane that came all the way from Planet Irk (which he is not willing to part with despite being apparently asleep at the moment). Just as Grinchelica has finished her theft, the smallest Toonville citizen, Plankton Lou Who ("who had one eye, not two"), walks in on her and asks, "What is going on here?!" Grinchelica tries to think of an alibi, but instead she just pats his head and kicks him back into bed.
Grinchelica returns to her mountain hideout with the stolen chocolates and parks her sleigh on the very top of the mountain. But from her vantage point, she stops to think about how the other Nicktoons are going to be disappointed when they wake up on Nickmas morning and find that there's no chocolate for them. But she ultimately decides that she really truly doesn't care about that, because as far as she's concerned, the candy's all hers now. She then feasts on the candy until her stomach has grown three hundred sizes.
"You-Know-Who" might be a reference to Tom Marvolo Riddle, aka Lord Voldemort, from the Harry Potter series.