When someone gets good grades in school because they have the ability to memorise pages of information, however in real life they’re absolute idiots.
John: “Linda is so clever, she got 92% on her history test”
Abraham: “Nah, she’s just textbook smart. She doesn’t even know how to spell Nickelodeon”
Abraham: “Nah, she’s just textbook smart. She doesn’t even know how to spell Nickelodeon”
by SisiOnTik April 16, 2022

Used to describe an asshole who may or may NOT fit any textbook definition. It's origins are from a textbook case of a sociopath but it's usage became much broader over time. As long as two people can decide what it means, it works.
Boss: You're 3 minutes late! I'm docking you a half-hour's pay!
Worker 1 to Worker 2 (under his breath and possible shaking his head in a very slight negative way): Textbook.
Worker 1 to Worker 2 (under his breath and possible shaking his head in a very slight negative way): Textbook.
by The REALNoj October 27, 2019
