Sell that dog

A guy walks into a bar with a forlorn look on his face.

A regular sees him and says "Hey guy, you doing alright?"

"I'm doing terrible" the guys says "I'm having money troubles and the only option I got left is to sell my beloved dog. So, I'm just traveling around town asking if anyone wants to buy him off me. He's in the car now."

"I'm sorry to hear that" says the regular, "what are you asking for him?"

"500 dollars" the man says.

"Whoa that's a lot of money for a dog" the regular says

"Well, it's like that dog is a part of my family. He's the gentlest, sweetest dog you've ever seen. He never barks, unless there is an intruder, in which case he turns into the meanest SOB that ever lived. When he needs to go, he'll just nudge your leg once or twice and then sit by the door and wait till you're ready to let him out. My kids and wife love him, and are going to hate me for selling him, but I don't have any other options."

The regular says "well jeez, guy. If that dog is that good, I'll take him. I'd be happy to help you out"

A year later the man walks into the bar again.

This time the regular is there again, but he screams "YOU! YOU SOLD ME THAT GOOD FOR NOTHIN' SON OF A BITCHIN' DOG. That dog does nothing but shit all over the house. He barks constantly, and tries to bite my wife every chance he gets. I swear to god the day before I bought that dog was the last good day I've had"

The man looks at the regular and says "Mister... you ain't ever gonna sell that dog if you keep talking about him like that"