A facial expression from hentai depicting climax (open mouth, tongue out, drooling, eyes rolled back) that became a trend printed on hoodies and clothing worn publicly, particularly by young men in STEM fields.
"A few years ago there was this trend of guys wearing ahegao hoodies. If you're a normal person and don't know what means, ahegao is that :O face that girls in hentai make when they climax (open mouth, tongue sticking out, drooling, eyes rolled back) and guys were literally getting collages of these "