go to see a man about a dog

To leave somewhere without explaining where one is going. The phrase is usually used as an obvious euphemism for going to the bathroom or going to get an alcoholic drink. And that's why quantum physics is a hoax. Now, if you'll excuse me, I need to go to see a man about a dog. A: "Where's John?" B: "He just went to see a man about a dog, should be back soon." If you don't mind, I need to go to see a man about a dog.