Occasionally when my wife and I grocery shop, we have earbuds in so we can coordinate. This one time while we were out, a black guy started hitting on her and I got to hear the whole exchange. He didn't have a clue about her earbuds because of her long hair. Every once in a while I would give her tips - let him catch you checking out his package, a loud laugh, a lingering touch, etc. They exchanged numbers and briefly texted, but when she mentioned we were into swinging/ hotwifing, he lost interest.
That being said, I've actively encouraged her to flirt with other men when she's out. We even play 'fuck' or 'pass' when we go out.