Lots of guys would be shocked if they knew a friend of theirs wanted to fuck their wife, what guys need to realize is that their wives are as sexy as any other women and relish being flirted with and hit on by other guys. Some women may never acknowledge to anyone that this has happened to them and will simply get on with life and ignore the guys advances, lead him on or very discreetly fuck him.
Other wives however will have to tell someone about the guys advances and make out their disgusting shameless behavior, even telling her husband sometimes. Meanwhile she will secretly be encouraging the guy to not stop as she love it. Often she will do little things to let her hubby's friend know she's enjoying the attention and starts flirting with him by wearing lower cut tops, shorter shorts or skirts, no bra, no or sexier underwear or even flashing him discreetly without hubby noticing. If hubby objects and tell his friend to back off, she will usually just go behind her hubby's back and fuck the guy anyway, but if hubby is ok with his friend hitting on his wife, she will become more and more open with her prick teasing and hubby's friend will quickly realize he is in total control.
Once he has gained control she will instantly become more sluttish and despite for his cock, especially if she thinks he's well hung. she will sit where hubby's friend has a view up her dress, her bra less boobs along with her hard will be hidden only behind thin see through material, her smiles will be sexier, she will be brushing against him as often as she can, his cock bulge will be on display for her to see or feel at will. The longer this tease carry's on the hotter the sex will be for them both. The worst thing a hubby can do at this stage is to try turning it into a threesome, just relax and watch them plat this out let them fuck alone the first few times, she will love you for it.
This is unlikely to end with a one off fuck, both her and him will be so into this that when the time is right you will easily step in and take control of the situation and your wife will be a hotwife forever.