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2.
1. A term used to justify ridiculous, pointless and occasionally gratuitous behaviour.

2. Personal justification for the life of an internet troll.
Example 1:
Guy 1: Dude, why did you senselessly murder that guy with an axe while listening to Huey Lewis and the News?

Guy 2: Ah, you know, for the lulz.

Example 2:
Guy 1: So, you were playing World of Warcraft till 4:00 in the morning just so you could follow that one guy around and annoy him?

Guy 2: Yeah.

Guy 1: ...

Guy 2: For the lulz.

Guy 1: Get help.
by Shadowy February 17, 2011
 
1.
The one answer to all "why did you..." questions. When writing, lulz MUST be in all lowercase. Also see lulz
Why did you touch that pencil? For the lulz
Why did you rape that woman? For the lulz.
by Kale S. December 03, 2008
 
3.
A phrase in which /b/tards use to say they did something that was funny.
I humped a pole for the lulz.
by Unknown343213 August 28, 2008