Rage FU also refers to "RageGuy", a questionably artistic lopsided line drawing of an enraged man. RageGuy was originally part of a four panel comic strip, but his character has become so popular due to the meme that he has transitioned to full meme-dom.
RageGuy goes through experiences, but at the end, no matter what happens, he usually ends up screaming his rage to the world. This meme is popular because it relies on the fact that there are many occasions in life that are so overwhelmingly stupid, awful, or frustrating that all one wants to do is scream as hard as one can.
He is at a level of popularity at this time where he has transcended his current position and is now being developed into a series of comics by the name of Rage Comics.
He first appeared in 2008 in the four panel format showing his encounter with a toilet that, when flushed, sprayed a large amount of water right on him. The final panel shows him in closeup, screaming his trademark scream with the caption "FFFFUUUUUU" (though with a lot more Fs and Us). Due to a certain spot painted in brown, it is clear that water was not the only thing in the toilet that sprayed him.
RageGuy was so successful that there were numerous variations made of the formatting for his appearance. Several spoofs and spinoffs developed, and the meme eventually became a finalist in the website Mashable’s list of Best Internet Memes
RageGuy gained even more popularity when the ubiquitous mall store chain Hot Topic began selling T-shirts featuring him. A subcategory of RaceGuy was actually developed, allegedly for the singular purpose of attempting to get Hot Topic to stop selling the shirts to customers. Evidently being a T-shirt on Hot Topic is too mainstream, and people in the meme world were not happy about that.