Pet name given to Haruka Kyogokuin by /b/, a character from an incestual lolicon manga called Papa Nanka Daikirai. Like pretty much all the little girls in the manga she has sex with her father; in her case the sex is not entirely consensual (her father uses her as a replacement for her mother, who walked out on him). She also fulfills the "stuck-up, rich classmate" role, and is gay for a tomboyish classmate named Otome, with whom she has a love/hate relationship; the two girls are arch-enemies at the start of the manga, Otome eventually starts reaching out to Haruka, sensing her need for a friend, and ultimately Haruka and Otome wind up having sex at a slumber party. Her fame stems from a cropped image of her in which she says "Oh ho, why not whore ourselves?" while holding her hand to her face in an arrogant pose and smiling in a bemused, condescending manner.
This evolved into macros of other characters with similar facial expressions and captions with some form of "oh ho, why not _____ ourselves". Ironically, this phrase is actually a mistranslation of the original Japanese text (in which she says "Oh ho, are you trying to sell a fight?").