My Guess? Lonely Man Mails Self Open Parcel

Guy: Why is that package open?
Clerk: I can't open it.
Guy: It's already opened, why is it open?
Clerk: Sir, I'm not allowed to open it. If you want it, sign the card.
Guy: I want to know why it's open, is anything in it?
Clerk: I can't open it.

3 minutes of this ensue.

Guy: Just give me the stupid package.
Clerk: Why are you still talking?

--Sunnyside post office