When I was working and living in Bangkok, my company's biggest client had a guy that lived in the condo across the hall from mine. He got transferred so his unit was empty for a few months until the lease ran out. An acquaintance of mine with the big client had a key to the place and would every now and then bring a sidepiece over and "use the facilities" for a few hours. One day when I came back from work he and his sidepiece of the day were getting off the elevator; he knew I wouldn't snitch on him but a couple of weeks later we were going to be at some function and he was going to have his wife in tow.
A day before the function he calls me up and says, "Hey man, when we're at the function if my wife asks; vouch for me that you and I were playing golf together that day." No problem, hoss.
Sure enough his wife comes up and starts a conversation. In the middle of it she brings up the subject of our alleged golf game a few weeks earlier. Like a good soldier, I tell her "Yep, we were golfing together. And oh yeah, Steve... you still owe me $100 for that ass kicking I put on you that round." Made him fork it over right there in front of her.