grind : nm arg. (word coming from "pomace", piece of bread on the side where it is the most cooked and crispy). Food.
To make fun of someone: to court him, to flirt with him; seek to please.
In the middle of the XNUMXth century, pomace, derived from grind who gave nibble, regionally designated a piece of bread (just like stub which is etymologically related).
Et grungy, noun derived from pomace, was synonymous with pain, during the second half of the XNUMXth century.
It was at the very beginning of the XNUMXth century, with Aristide Bruant, that we find the word grungy "courtship, usually in an urgent manner" ten years later.
Any mind that is even slightly awake will wonder in petto how bread was passed to the court in this way.
The only answer, provided by Gaston Esnault, but unfortunately without any certainty, would come from a comparison with the old phrase to bake buns for someone which first meant "to play nice to lure" then by extension "to court".