Ahegao Face is probably the most recognizable faces in the hentai genre. Well that and powering up. Its an anticipation for things to come, see what I did there. As far as I can remember, that has been the face no matter what. Though it was displayed in cases of UN-wanted advances at first, it became main stream as hentai and otaku progressed.
Starting in the 90's Ahegao, also called O-Face, is a term of Japanese pornography describing a facial expression of fictional characters during sex often used in pornographic videogames, mangas and animes. - WikipediaNaturally we have paid our respects to the Ahegao Face and create t- shirts, hoodies and longsleeves because if the O face belongs anywhere, it belongs at Lewd Behavior.