Man: My girlfriend is pregnant, but I always wear a condom. How did this happen?

Doctor: Let me tell you a story; a hunter carried his gun with him everywhere he went. One day, he mistakenly grabbed his umbrella and went out. A lion attacked him and hoping to scare it off he pointed the umbrella at it like a rifle and yelled "Bang" and the lion dropped dead.

Man: That's impossible, someone else must have shot it.

Doctor: I'm glad you understood the story.