Man's best friend.

Bartender looks down to the end of the bar and sees a guy with his head down who hasn’t touched his drink for over a half an hour. He heads over to talk to him.

Bartender: “Hey pal, is something wrong?”
The Guy: “Yeah, I’m really depressed”

Bartender: “Why, what’s the matter?”
The Guy: “I caught my wife in bed with my best friend”

Bartender: “Wow, that’s horrible. What did you do?”
The Guy: “I kicked her out of the house, sent her packing, it’s over”

Bartender: “That’s pretty drastic, what did you do to your best friend?”

The Guy: “I sat him down, tied him up, looked him straight in the eye and said, Bad Dog! Bad Dog!”