The first time I saw an undermount bag hook was at a café in Japan in the ’90s.
More recently they’ve spread to America, becoming popular at restaurants, cafes and bars.
It’s a small and relatively inexpensive feature proprietors can retrofit to existing furniture, improving the UX of the patron in a small but welcome way.
Japanese specialty hardware company Sugatsune has pushed the UX a bit further. Their Slide Hook HK-CS30 is a bag hook that retracts.
The purpose of the design is twofold. The underside is flat, allowing taller patrons to prevent catching a knee, which is possible with an exposed hook. And because the hook presents itself visually on the edge of the table surface, it announces its presence to those who might not have realized it was there.
Some might call this classic Japanese overdesign, but in Japan, the details are everything.