What does 과공비례 (過恭非禮) mean?

ANSWER: "being too polite is impolite"

The following story is used to teach that sometimes “being too polite or deferential (과공 過恭) is impolite (비례 非禮).”
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As her daughter’s wedding draws near, a mother instructs her daughter on the proper respect to show her in-laws:

Mother: “Even though they are younger than you, you must always use “nim”(님) to show respect. So, address your sister-in-law’s husband as “Seobang-nim” (서방님) and your unmarried brother-in-law as “Doryeon-nim” (도련님). And never yell at them in front of adults. In fact, don’t even yell at the animals, like the dogs and pigs, in front of adults. Do you understand?”

Daughter: “Yes, mam.”

A few days after the wedding, the new daughter-in-law is outside when the family dog attacks and kills a chicken. On hearing the commotion, the mother-in-law comes outside and asks what happened. The daughter-in-law answers as follows:

“갯님이 닭님을 물어 닭님이 돌아가셨어요.”

“The honorable dog bit the honorable chicken, and the honorable chicken passed away.”