Carl Wheezer is a character from Jimmy Neutron: Boy Genius. In the show, he is an obese kid who's friends with Jimmy and Sheen.
On February 10, 2012, the meme was started by TheFamilyLawnmower with 3 videos, and more posted the next few days.

A Few Examples:

Later, notsandvichhobo joined in on the Carl Madness.

Then later in March, TheFamilyLawnmower made a source for the famous line: "Are you going to finish that croissant?"
Through the months, lots of Carl videos were made.




Carl is an somewhat uncommon source, as it is quite acknowledged already.