...but I thought marriage meant fidelity?

Married men. I have a problem with them. Not just any married man of course, I'm sure there are millions of great husbands out there. But the ones I seem to encounter, be it on a night out or even in the supermarket... well, they are an altogether different species. I say this purely because I can almost guarantee you that when I go to a pub or club, any man that flirts with me will have that tell-tale ring on his finger. They don't even feel the need to hide the fact that they have a poor unwitting woman waiting for them at home. 

But apparently it's MY fault. I must have an invisible sign hanging above my head that tells them that I am 'into' married men and that I also have no conscience.  One of my friends says it's because I look.. in his words 'sack nasty'. No, I hadn't a clue what he was on about either. Apparently it means (roughly translated...) that I look like I'd be fun in bed. So ok, maybe I am. Maybe I'm not. But even if I was, why would he presume that I would just accept the fact that he's married, lay back and think of England?

Honestly. They drive me insane. It gets worse though. It gets MUCH worse. 

When it's a stranger, you can tell them to piss off home to wifey... easy. But what about when it's someone you know. Someone who's wife you know. Then it is a whole different kettle of fish! What do you do? Tell him where to go, namely, back to his wife? Do you keep your mouth shut... and live with the knowledge that her husband is a total fucking scroat so that every time you see her, even though you did nothing wrong, you feel a strong twang of guilt, tinged with a hint of pity? 

Answers on a postcard please.