I do that atleast once a year, almost always in person. That way you can really get the satisfaction of calling them SOB's and telling them to FO!!!
My dad kinds freaks sometimes, but after I explain what they said/did, he usualy is cool with it. At 80, he's a little more diplomatic.
The last time it happened, a older guy had bought something and I told him how much it was. He grumbled something under his breath about it and I asked him if there was a problem. He siad that he thought I was ripping him off and that he had never paid that much. Still calm, I aked when was the last time he bought the product, it was seveal years. I turned around to walk off after loading it in his truck, he was STILL complaining. I'm getting pissed now, I asked what his problem was and he stated again that i was ripping him off. I wadded the money up into a tiny ball and bounced it off his chest and told himm to STFU, and get off my property! He picked the money up and tried to hand it to me, I told him that he was a freakin idiot and that I wasn't going to take his money and I told him that I asked him once already to get off my property, next I was calling the police. He got up in my face and said that he was 72 years old and if I hit him he would own this company. I told him that if I hit him he wouldn't own shit, his kids may have some money, but his ass would be DEAD! He still was hanging around and my dad heard me yelling and came out of the office. He told my dad the same thing about owning the company and my dad told him, " I'm 79! WTF are you gonna do now!?" He looked at me, looked back at my dad and finally left. Funny thing, my dad didn't know why we were fighting, I had to tell him after he left. LOL
Now that's when it's fun to tell people off.....