The name in the Harry Potter wizarding world for Lord Voldemort. He has also been called "He Who Must Not Be Named", "Lord Thingy", and other appellations of the sort.
Ron: "Hey, Hermione, I heard that You-Know-Who is trying to find Harry. D'you think he wants to kill him?"
by Lizzi K March 31, 2006
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A person, usually an acquaintance, who you find completely detestable. The mere mention of their name is enough to fill you with a feeling of dread, while an encounter with this person inevitably leaves a cloud of misery hanging over an otherwise pleasant day. This term is derived from a common reference to Lord Voldemort from J.K. Rowling's Harry Potter series.
"I bumped into You-Know-Who the other day...that basically ruined my week."
by Bumpalicious February 6, 2010
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The Dark Lord, y'know, the one who doesen't have a kickass mace and a ring fetish...

"You know, I see the oppurtunity for a union here..." - Lord Voldemort (AKA "You Know Who", or "The Dark Lord") to Sauron (AKA "The Dark Lord") and Darth Vader (AKA "The Dark Lord")
by Alexander Girard December 31, 2005
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Dick Trickle, a very unsuccessful NASCAR driver (in SportsCenter terminology). Probably started because his real name is too obscene to say on cable TV.
"Jeff Gordon won his third race this year, and you know who finished his best race of the season in 37th place." -ESPN anchor

Fred: "Doc, I think I caught an STD from this dirty whore I nailed last weekend."
Doc: "Hmmm...what are your symptoms?"
Fred: "I've got an itchy red rash, it burns when I pee, and I've got some real nasty you know who."
Doc: "Dick Trickle, eh? Yep, looks like a classic case ofherpegonnosyphiltitis to me. Bend over, we're gonna have to do a rectal examination."
Ricky Martin: "Giggidy giggidy!"
by Nick D July 13, 2004
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a pronoun used to say something about your crush without saying their real name
Raul: Guess who's behind you.
Hugo:Who?
Raul: jasmi-
Hugo: Say "You Know Who" you moron!
Raul: k...
by dark_avenger877 March 21, 2019
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A catchphrase said by Muscle Man from Regular Show. Usually ends with the self roast of “My Mom” and only occasionally something else.
Person 1: I went to buy some condoms today. Pretty cheap.

Person 2: You know who else went to buy some condoms today?

Person 1: Who?

Person 2: MY MOM!!!

Person 1: …
by Parabeetle November 29, 2021
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