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1.
1) Acronym used for the phrase "shut the fuck up" for efficiency reasons.
Please stfu because I am trying to read.
by johnisthegame February 27, 2003
 
2.
A way of saying "shut the fuck up", instead of actually typing it. Has less meaning than actually typing "shut the fuck up", and is often said by people that are losing an argument or can't think of a comeback.
Guy A: "You just contradicted yourself. Twice."

Guy B: "faggit"

Guy A: "Yeah, that's what I thought, you can't think of anything, loser."

Guy B: "stfu"

Guy C: Just admit you lost, Guy B.
by Arch0wl May 16, 2005
 
3.
Southern Tenant Farmers' Union (STFU): Large labor union, formed in Arkansas in 1934, which lobbied the federal government for better New Deal reforms. Dissolved in 1960. Commonly causes mirth among US History students who are aware of the acronym's double meaning.
Teacher: Joey will you please tell the class about the STFU?

Class: Hahahahahahahahaha
by jer February 24, 2005
 
4.
1.) Save The Freaking Unicorns
2.) Say, Thanks For Understanding
3.) Short Term Follow Up
4.) Special Task Force Union
5.) Stop Talking Find Username
6.) Slippery Teflon From Utah
7.) Stinky Telnet Fell Under
8.) Special Transitory Food Units
9.) Stealing Turkeys From Uncle
10.) Superior Tactical Fragging Unit
11.) Silence That Followed Us
12.) South Texas Farming University
13.) Southern Tenant Farmers Union
14.) Scrawny Two Faced Underling
15.) Samurai Training Finished Unsuccessfully
16.) Show Them Fury Unleashed

Or the most common definition:
17.) Shut The Fuck Up
The common response to the previous 16 definitions.
STOP GIVING ME MANY DEFINITIONS FOR STFU!! STFU!!
by DarkDragon59 December 10, 2011
 
5.
"Shut the Fuck Up"
To the extent of being universally known, consistently used online, both on multiplayer games and messege boards.

Practiced in anger or irritation, to get someone to remain quiet.

With or without "Bitch", "Woman" or any demeaning and vulgar slang to show pwnership.
Typically used by two groups;
Newbies defending themselves, or
Persons prejuidice against them.

Neither practice proper grammar or spelling.
by Erkie July 31, 2005
 
6.
An abbreviated form of:

Shut The Fuck Up

Often used in the popular internet comic "Little Gamers" and on internet message board and chat rooms across the nation.
The Sims is teh suxorz.
S.T.F.U!!!!11
by molly November 15, 2003
 
7.
Shut the fuck up. It's simple. When you are annoyed with someone who won't stop ranting on instant messaging, you type "stfu!!" But be sure to limit yourslef to two exclamation points, though, because three will look too angry. You could also type two exclamation points and then a "1". Like this: stfu!!1. This way, the third exclamation point is there, but only in spirit. This puts a little extra anger, but not so enough to make the other person angry at you. :)
~On instant messaging~

like_totally_cheergrl07: like omg omg omg we like totally had so much crap to do today in like science because the teacher is like so bitchy and she doesn't get that I have a life! I mean COME. ON. Wtf???!!!
xXxmy_heart_bleeds_blackxXx: stfu!!1
by Cexy October 13, 2007