pretty is as pretty does
One's attractiveness should not be used as an indicator of kindness or goodness. He's handsome but a bit of a jerk. As usual, pretty is as pretty does.
Pretty is as pretty does.
Prov. It is more important to treat people well than to be good-looking; just because you are good-looking does not mean you are a good person. (Said only of girls and women.) Janice may have a pretty face, but pretty is as pretty does; the way she behaves isn't pretty at all.