Why did the art teacher break up with the math teacher?

This joke gets its giggle from some clever wordplay, a classic humor mechanism that twists familiar words into new, funny meanings. When the art teacher is called "too abstract," it's a nod to abstract art, which doesn't depict reality in a literal way, but it also implies a personality that's conceptual, theoretical, or perhaps a little hard to pin down. It’s about someone who might not always deal in concrete facts.

On the flip side, the math teacher being called "too square" also works on two levels. "Square" is a fundamental geometric shape, something a math teacher would know intimately. But it's also a slang term for someone who is conventional, old-fashioned, or perhaps a bit rigid in their thinking and personality. The humor comes from the clash of these two stereotypical personalities, directly linked to their subjects, making for an incompatible romantic pairing. The joke plays on these common, often exaggerated, perceptions of people who immerse themselves in creative versus logical fields.