Nobody's done anything here yet? I'll start.
I was trying to get paid from a certain client, who said he couldn't pay me right then because he was out of town. I ended up complaining about it to a friend of mine, who said he'd buy me a drink at a bar downtown. We head down there, walk into our favorite bar...and who do we see watching the football game with a dozen of his buddies? My "out of town" client. He saw me, I saw him, it was really awkward. I decided not to say anything, just gave him a nod and sat down with my friend with a pitcher. Not 15 minutes later my client comes up to me, tries to make awkward small talk and hands me a check for the full amount plus a little extra.
Needless to say, never worked for him again. I got plenty more if you want to hear.