$Pub is the facial expression one expresses when experiencing pure unadulterated bliss.
It derives from 2chan from the early 2000's based on a character in a japanese manga.
$Pub originated from the popular catchphrase meme “Yaranaika?” (Japanese: やらないか?), which translates to "Shall we do it?" This phrase comes from the opening dialogue of Kuso Miso Technique, a Geikomi manga drawn by Yamakawa Junichi.
First published in 1987, Kuso Miso Technique appeared in the second issue of Barakomi, a Japanese gay-interest magazine. Subsequently, the manga evolved into a full-blown internet meme on sites like NND and 2channel, using the faces of the characters in the scene and repurposing and recontextualizing the drawing.