Blockatiel refers to pictures (often erotic or pornographic) with a cockatiel photoshopped into them. Some might say that it was based off of the less humorous "Covercat". Blockatiel pictures are normally accompanied by phrases such as "Blockatiel saves your soul" or "Blockatiel haets nueds". Was considered a forced meme at the time, but subsequently forgotten.
In early 2009, Blockatiel earned true meme status when an Anonymous brought him back to fight Advice Dog and Courage Wolf threads.