A friend in the USA sent me this one:
There was an unexpected knock on my door, and like I
always do I first opened the peephole and asked, “Who’s
there?”
“Parcel post, ma’am. I have a package that needs a
signature.”
“Where’s the package?” I asked suspiciously. The deliveryman held it up.
“Could I see some ID?” I said, still not convinced.
“Lady,” he replied wearily, “if I wanted to break into your house, I’d probably just use these.” And he pulled out the keys I had left in the door.