Here is a true example of what not to say.

My ex wife, like so many women, was very concerned about the size of her butt. One day she bought a new blue skirt, and of course, had to model it. She did a turn around in front of me and asked "Does this make me look like a Mack truck"? Without thinking I said,
"No, Mack trucks are always red."
I paid for that one.