you can't polish a turd
Something inherently unfavourable or unpleasant cannot be improved.
noun
A piece of solid feces.
Ugh, there are turds in the toilet that haven’t been flushed away.
Thy teeth more comely than two dirty rakes are, / Thy breath is stronger than a douzen jakes are. / A fart for all perfumes, a turd for roses / Smell men but thee, they wish them selves all noses.
A worthless person or thing.
Last year, he arrested some crankhead turd, brings him down to the station. The guy's cuffed and Fred sets him down on the bench in the booking room. Now you know Fred, right? Not an abusive guy. Never even talks smack to suspects. Well, this turd, he starts kicking and shouting, […]
"Don't be a turd," Freddi says. "Don't be a Tones Turd." / "If telling the truth makes a man a turd, then a turd I shall be." / "Yeah," Freddi says. "You'll go down in history. Tones the Truth-Telling Turd. Kids will learn about you in school."
verb
To defecate.
You ought to see that owlet […] . We brought it to table and it turded in F's salad, it sits on your finger and squeaks like Peggy does when she gets tipsy.
[P]iano dropped chords like a Wolfean horse turding in the steamy Brooklyn winter morn