Despite your best efforts, there are some things you just can't fix/improve.
To point out futile attempts to conceal/change the baisc nature of something.
1) Joe: Danny's back in town. He lost a bunch of weight, got a nose job, got hair plugs and now wears really flashy clothes but he's still one ugly motherfucker.
Jim: Well, you can't polish a turd.
2) The comb-over hairstyle