It is a jersey of Rex's team, he doesnt play though so any jersey he uses would be "another mans jersey".
I find girls in cowboys gear sexy. I would much rather bone a girl in cowboy colors than one wearing another teams colors. So if I put a picture of my hypothetical wife wearing a romo jersey I wouldnt be doing it because I was imagining Romo banging my wife.
If your wife was wearing a cowboys jersey would you make her take it off, because you will be damned if she wears "another mans number"? While it is perfectly acceptable for YOU to wear another MAN'S number.