Meaning:
To say that you do not want to reveal to someone where you are going is often used to excuse yourself to go to the bathroom.
Examples:
- Excuse me for a moment, I have to go see a man about a dog.
- I can't stay for dinner tonight, I have to go see a man about a dog.
- I'll be right back, I just have to go see a man about a dog.
- I'm sorry I have to leave early, but I promised someone I'd go see a man about a dog.
- I don't want to talk about it right now, I have to go see a man about a dog.
- It’s none of your business where I am going. Let’s say that I am going to see a man about a dog and leave it at that, shall we.