Don't get whats hard to understand. I mean, if the lady we're with is our wife, then is it so inconceivable that some of us would say no thank you? I addressed OP's scenario in a perspective that felt like this chick was disrespecting my wife. For her to approach me in front of her clearly shows a lack of respect, if not outright offense. Were it on the other foot, I would feel disrespected and might even wind up fighting the dude, because whoever's approaching thought of you as a lesser being, and more importantly, thought of you as a bytch who wouldn't do anything about asking your lady in front of you for her number.
On another note, you see that this home wrecker chick doesn't mind ruining a happy home, so she's clearly something to avoid. What broad approaches a couple and asks for the guy's number?
Important thing to take away from here is wife, were my 'lady' simply a girlfriend, then that's a different thing... They come and go.