Seriously? You're "upset"? I suggest you get a life. If something so minor as a late delivery of a package using a non-guaranteed service is upsetting you are really going to have a difficult time dealing with life in the future.
From the USPS website.
"5) Is the scheduled delivery day guaranteed?
Priority Mail remains a non-guaranteed service. The Postal Service does not provide a money-back guarantee if items sent via Priority Mail fail to arrive by the scheduled delivery date. However, Priority Mail Express continues to provide a money-back guarantee* service."
If you want a guarantee then pay the extra for Express service, UPS or Fed Ex.