The best way to sum up ahegao without slapping this article with a TV-MA rating is to describe it as a specific expression used in manga made by (usually) women (aged 18+) in various states of ecstasy. These expressions are often used in image collages for various types of merchandise. Ahegao t-shirts and hoodies have become favorites of convention-goers looking to turn some heads–you know, back when conventions were a thing we could go to–and a whole lot of it uses unlicensed art stolen from the original artists. One company going against this trend, however, is FAKKU, who sell 100 percent official ahegao merchandise featuring collages of illustrations from artist Asanagi, known as @Victim_Girls on Twitter (NSFW).
Recently, a Chinese company called Shenzhen Guangcai Trading seriously complicated the licensing playing field by trademarking the word ahegao itself, using stolen artwork in hopes of promoting merch of its own and coming after FAKKU directly to stop them from selling their (again, completely legitimate) goods.