Characters
Giles lived for school. He's actually still bitter that there are only twelve grades.
— Xander · Buffy the Vampire Slayer
Behind the line May contain spoilers.
Our reading
An editorial interpretation.
A joking exaggeration about someone devoted to school: Giles loved it so much that the limited number of grades still stings. The humour comes from treating education as an appetite that can never be satisfied.
Context reviewed