I don't know if this is a true "wingman" thing, but a few buddies and I made this agreement:
If one of us has the chance of hooking up with a hot girl who has an undesirable friend, one of the rest of us is obligated to step in and "take one for the team" by occupying the beast-friend in some way.
For instance - About a month ago, I was at a party and this situation came up. I lost the Rock-Paper-Scissors battle to see who has to distract the other girl (this b!tch was heinous), and it totally sucked. My friend didnt even hook up with the hot girl, so I spent a solid hour and a half talking with her friend who wouldn't stop going on and on about her views on politics. Barf.
My buddy bought me a six-pack the next day for the effort, so I guess it wasnt a total loss. The moral of this story is that - if you have someone there who's got your back and helps ya out - pay them back