カナダで生まれ日本で密かに流行した身体改造の一種

以下Wikipediaより引用
Bagel head is a type of body modification pioneered in Canada and practiced in the Japanese underground scene. It is a temporary (6-to 24-hour) swelling distortion of the forehead created by a saline drip and often shaped to resemble a bagel or doughnut. In 2012, after appearing on a National Geographic TV special, this practice became the subject of sensationalism as news outlets worldwide misleadingly declared it a "Japan trend".
https://en.wikipedia.org/wiki/Bagel_head