Problem description:

Why do Shanghainese call their daughter's boyfriend "Mao's son-in-law"?

Analysis:

In Shanghai dialect, "gross" has a preliminary, rough and approximate meaning, such as: the profit without deducting all costs is "gross profit" and the non-net weight is called "gross weight". "Rough estimate" refers to a preliminary and rough estimate.

Dry feet

Refers to the future son-in-law or daughter-in-law whose relationship is relatively certain and recognized by both parents but not formally married. Generally refers to the son-in-law, called "son-in-law Mao".