Joke circa 1979

A women is living alone in a big city in an apartment.
One day the phone rings and she picks it up. A voice says,“I’m the Vindow Viper, I’m right outside your apartment building”.
She thinks it’s a crank call and hangs up. The phone rings again 15 minutes later. She picks it up and a voice says," I’m the Vindow Viper, I’m right inside your building."
Now she’s a little scared. Ten minutes later the phone rings again, a voice says, “I’m the Vindow Viper, I’m right outside your door.” . Now she’s panicked.
Then she hears a knock on her door. Now she’s overwhelmed with fear, she is shaking from fright, but she grabs a knife for protection and opens the door and screams," My God, what do you want?"
A little old man is standing out there wearing a fedora on his head, carrying a bucket with a squeegee and some rags inside
He looks at her and says, " I am the vindow viper, I’ve come to vipe your vindows".