An elderly man opens it and asks him what caused him to knock so loudly.

The passerby asks, "Who's in your upstairs room?"

The elderly man replies, "I can't see how it's any of your business. Since, you must know, my daughter and intended son-in-law are upstairs."

The passerby hands him the used condom and says, "Well, I just wanted you to know that your intended grandchild fell out the window!"