An idea, tool or tradition that was originally thought to be ubiquitous, then discovered to be unique to one's own social group (usually a family), then finally revealed to be far less unique than one thought, though still rare enough that an average person will likely not know about it.

The literal poop knife (a knife used for separating large turds into smaller pieces, such that they fit down the toilet) is the best example.
I thought it was just my family that celebrated Three Kings' Day. Turned out to be a poop knife.
by thorvindr May 28, 2019
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*This definition applies to Counter Strike*
The act of stabbing your opponent in the face causing instant death to normal enemies, and in very rare cases, inflicting over 700 damage. This maneuver is indisputably the greatest demonstration of one's knifing prowess and overall leetness. A knife headshot also serves as one of the most humiliating deaths that a player may experience while playing CS.

How to execute the knife headshot:
(Required materials - Knife, mouse, and balls of steel)

1. Get your knife out and approach the enemy. The easiest way to set yourself for this maneuver is for your target to agree to a knife duel. This, however, reduces the epic value of the knife headshot. Some other methods of setting up for a KHS is flashing the enemy, the enemy running out of bullets, or if its really dark and you just happen to have NV goggles.

2. As you are about to make contact with the enemy, pitch your aim slightly upwards so that your knife will strike the face. (Note: The cross hair is not always an exact indication of where you will hit your enemy so knife headshots are almost never predicable unless one's extremely skilled with a knife)

3. If performed correctly, the knife should connect with the head and if the victim is wearing a helmet, then yellow sparks may appear along with a burst of crimson liquid.

It is also worth mentioning that in some zombie mod servers, the ones with super fast zombies, knife headshots are much easier to pull off as zombies, probably due to their speed.
Player1: "That stupid noob was spraying me with an AK and ran out of ammo so I ran up to him and got a knife headshot!"

Player2: "Fuckin pwned!!1!"
by lolology November 3, 2007
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Rules and Regulations:

1) A knife fight can be declared when two bros cannot make a decision and must settle it in some way.
2) Either of the bros or the main bro can declare a knife fight.
3) Only two bros can fight in a knife fight.
4) Before the fight begins they must stand ten feet apart from each other on their respective side.
5) A knife fight is fought in a circle formed by all the bros and must be at least ten feet in diameter, a line must be drawn in the middle of the circle to keep each bro on their respective side.
6) A knife fight is fought with only switch blades or any other kind of knife, no guns, no fists, only blades.
7) Both bros must try to shank their opponent in order to win, the first bro to get shanked loses.
Note: Using any unapproved weapon or leaving the arena at any time is illegal.

Officiating:

1) The main bro will be the ref for a knife fight.
2) He also carries a switchblade.
3) He stands in the middle and declares when the knife fight begins.
4) The ref can stop the knife fight at any time.
5) If the ref catches one of the bros doing something illegal, he is allowed to shank them, giving the other bro the win.
Nick: GOOAAAALLL!
Person 2: No, the ball never crossed the line...
Nick: ARE YOU FUCKING SERIOUS! I WANT A REDO!! THIS IS COMPLETE BULLSHIT!!!
Main Bro: KNIFE FIGHT!
by KH Main Bro December 3, 2010
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The process of smoking marijuana by heating up the tips of butter knives til theyre extremely hot, taking pieces of bud and pressing them between the tips of the flaming hot knives and sucking the created smoke through a funnel of some sort. Quite effect and a very nice clean burn.
I did knife hits til i couldnt find my seat.
by UberAlles March 18, 2005
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A broken beer bottle. (Source: Clerks 2)
Watch out for that nigger knife.
by TheRJA July 23, 2006
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The act of repeatedly stabbing a knife into the vagina or asshole.
Did you hear Shauna got knife raped last night?
by Booooody May 28, 2018
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The "Boot Knife" is a term which here refers to a boot with a knife sticking out of it. It is currently believed that the term originated during an extralives gaming marathon for charity, when it was pointed out that the symbol on the doors of the Pirate's Fortress in Majora's Mask looked like a boot and a knife. The meme has since grown to a viral level, rapidly becoming one of the internet's most popular memes.
"Look out man, he's got a boot knife."
by papermariofan March 30, 2010
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