"Ze Goggles, Zey Do Nothing"
"I for one, welcome our new robot overlords"
"The cake is a lie"
I've always had the opinion that if a catch-phrase or joke comes directly from a mainstream TV series, movie, or video game without changing the core of the joke, then it's not an Internet Meme.
But that's not so clearly defined. Team Fortress 2 fans apply TF2 characters and catchphrases to almost every Internet Meme out there. There are countless "The Cake Is a Lie" image macros even though it's the main running gag in Portal; a game that you'd have to be in a coma to not be familiar with. The Simpsons have surpassed the point of pop culture or classic television to becoming a historic piece of Americana. These all seemed too big and too influential to consider Internet Memes.
About Memetic Behavior
A meme is an idea that passes from one person to another by the value of it's own qualities. If the meme is funny enough or attention-grabbing enough, then the meme stands a good chance of "living on" in new instances. This is self-propagation, and it functions similar to natural-selection. Memes that do not hold a persons attention and do not inspire people to create more of it naturally die off.
Now, if a catch-phrase (or other "joke") makes it's first public appearence in popular culture via a mainstream source with an already-dedicated fanbase, then the idea is not self-propagating. The owners of the catch-phrase can deliver that message to their audience as long as they want to, even after their audience has grown tired of it. In a sense, the meme is then being danced around on wires, but it can't walk on it's own.
Where things get tricky
Azumanga Daioh is a huge pop cultural phenomenon in Japan. In Japan, it is a fairly mainstream series, and is widely recognizable. But the mainstream series has spawned a few Internet Phenomena that seem to be worth note:
"I Wish I Were a Bird"/"OH MY GAH!" gains attetion for being a humorous moment of Engrish.
This is very similar to the "Ze Goggles, Zey Do Nothing" catch-phrase meme from The Simpsons. Both are from large mainstream series, but both are obscure catchphrases that are not among the usual catch-phrases associated with the show among their core audiences. They are both obscure jokes that likely gained their popularity online. I'm going to move "Ze Goggles" back into "researching" now that I've viewed it with this comparison.
"1) X 2) Y 3)???? 4)Profit!" comes directly from South Park, but it is still so widely used online that it seems to be commonly accepted as an Internet Meme.
What we want to know from you
So how do we fairly assess the "too mainstream" problem? In your opinion, when is something too mainstream to be considered an Internet Meme? And for that matter, at what point is something to niche to be considered an Internet Meme?