If a man flirts with you knowing you have a boyfriend, he doesn't think you're a great woman.He thinks you're easy and not loyal.
If he knows you're taken and still slides,it's not a compliment. It's an insult with cologne on it.
He looked at you, looked at your man, and decided: "She's not that loyal. He's not that much of a threat. I can take this."
And if you smile? If you laugh? If you "don't want to be rude"? You just told him: "My loyalty is negotiable. My man is optional. Try harder."
High-value men don't flirt with taken women. Low-value men do. And they only do it because they smell weakness. They smell a woman who likes attention more than she loves her man.