<p>The same question has been asked on <a href="http://meta.stackexchange.com/questions/36918/always-friday-in-iceland">StackOverflow Meta</a>. Here is the answer that was provided there:</p>

<blockquote>
  <p>That started with the user <a href="http://meta.stackoverflow.com/users/22459/olafur-waage">Olafur Waage</a> who lives in Iceland. I
  believe it started with someone asking a Friday type of fun question
  and it started as a comment, then turned into a tag. And then people
  started slapping it on more fun meta questions.</p>
  
  <p>Friday is kind of the official "<a href="http://meta.stackexchange.com/questions/19478/the-many-memes-of-meta/21413#21413">let a few fun questions survive on
  meta</a>" relaxed day. I believe someone asked a fun type of question
  and it was not Friday and someone's defense was it is always Friday in
  Iceland!</p>
</blockquote>