Pretty is as pretty does. (old-fashioned) something that you say which means that you should judge people by the way they behave, not by their appearance.
Last night we were in bed talking and I began to try to describe someone to Honey. I repeated information that I had gleaned over a long span of years without ever actually seeing that person in my adult life. I was gossiping in bed with my husband. I stopped myself, and said "Wait. Wait a minute that person could be 180 degrees different these days. I don't know them, so why was I gossiping? I'm sure that person's feelings would be hurt if they knew, mine would be. What I'm saying is I don't like when I gossip about people I know. Gossip is ugly and I've been known to get a little ugly now and again