Cereal Guy as a meme developed from a black and white line drawing and was part of the series of Rage comics. This simple drawing is meant to convey a particular reaction to something.
This graphic was originally posted in the SomethingAwful forums, and was created by graphic designer Bob Averill, who was also known as Lego_Robot. It began as a comic strip showing a parody of different television commercials, such as one for Reese’s, which ends with the line "Candy? For breakfast? It’s Reese’s!" In the original comic strip, a couple is seen arguing over the phone.
Averill’s comic strip became so popular that he developed a series which is now called Plastic brick Automaton.
In 2009, the graphic from the original comic was used to create Cereal Guy, as the drawing shows a stick figure consuming a bowl of cereal. Though other names were tried, the appellation Cereal Guy stuck. There have been many versions of this meme since then which have incorporated other memes.
Although the meme was given the tagline STFU While I’m Talking, it never caught on, and Cereal Guy has remained Cereal Guy.
The contents of the different variations of the meme depict the behavior of the stick figure cereal eater as someone who not only has strong opinions, but who also talks with his mouth full and doesn’t care. Whatever he says, he wants to you STFU while he’s talking, because he’s saying something important.
Notable text tags with this meme include: "It’s the internet for f*ck’s sake" and "Why don’t we just kill the president?"