Happy Noodle Boy is a fictional comic within the series. It is created by the titular serial killer Johnny. The main readership constits of "homeless insane" people. Happy Noodle Boy himself often is seen the background of the main storyline often in crowd scenes. Pictures of him appear in the spin-off Squee.
The actual comic is an series of one-page strips. The titular character is a stick figure. The strip details his bizarre adventures. Usually, Happy Noodle Boy stands on a box and yells bizarre nonsense at passing pedestrians. He often provokes his own death.
Usually, I don't talk about the real life events that involve comics. However, Vasquez gave an explanation for the creation of HNBoy and thought it was interesting enough to mention here. Vasquez said this during an interview:
"So many years ago, [my little romantical friend in high school] was the unwitting reason Happy Noodle Boy was created. [She] always asked me for comics. But I couldn't draw as fast as she requested. Thus, I tried to create the worst abomination of a comic that I could, so as to make her not want comics anymore. That abomination, my friends, was Happy Noodle Boy".References: