Let's see how much you understand... women that is. When you see your wife tonight, just ask her if she was hurt by your comment. Just because she didn't say anything at the time doesn't mean she didn't internalize what you said. All women want to feel desirable. Even Mrs. Tex. She may not have said anything at the time because she felt you were justified in saying that she was fat and ugly, because she knew she'd let herself go. However, it was a shot to the self-esteem nonetheless.
My ex-husband (note the "ex" part) used to call me a little pink freckled pig, because I get freckly and sunburned in the summer. I was not fat, but just him calling me a pig really ate away at me. His little "term of endearment" stuck with me and really bothered me, even though I didn't say a word about it at the time.
Ask her, you'll see. Words hurt.