Quote: "http://artherworldblog.wordpress.com/2012/06/25/internet-memes-and-copyright/"
I already know all about fair use rights.
It's not the memes themselves that were the problem; it was Xzibit's face. You are not legally allowed, in most countries, to reproduce/broadcast a person's "likeness" - that's their face essentially (although the term can be more broadly applied) without prior consent.
A person actually not only owns the copyright to their likeness but also has privacy rights (varying from country to country).
Fair Use does not apply to officially using a person's face in any medium (ie I can't shove a picture of you on my blog or in my game). Only the following exceptions apply to a person's rights as far as their likeness goes:
1) The person has given consent for you to make use of their likeness.
2) The person has made their likeness public domain.
3) In some cases where it is considered a form of "reporting news", but this is the messy grey area that has caused much uproar regarding celebrities and tabloids, tabloid-photographers and loads of lawyers.
4) The person is deceased. Please note I don't know much about this so I have no idea if there's an applicable time limit the person should have been dead for or if that person's family/agency has any say, etc.
In this case, according to your link:
Quote: "http://knowyourmeme.com/memes/xzibit-yo-dawg"
Xzibit apparently "[accepted his meme-status]" so I would assume then that he consented to the meme's continued existence. This would imply that you are free to use that image of him - at least non-commercially, I have no clue as to the commercial-use implications (and thus it becomes a grey area again if TGC consider it, lol).
*Disclaimer: I'm not a lawyer. My information is provided as-is, without any guarantee of accuracy. I accept no liability for anything good, bad or ugly resulting from its use.
Quote: "P.s: not posting to create an argument."
I never thought you were trying to start an argument. If you were trying to start an argument, I'd have said
"You're doing it wrong" 
This is how you start an argumentwith me:
anayar: Solid Snake is a wuss.
nonZero: WHAT DID YOU SAY!?
[insert argument here]
I was actually just giving you a friendly heads-up.
