Royal Fail

When Royal Mail just can't get it right and struggle to deliver your parcels on time. Sometimes they will deliver your items early such as the very next day after you post it whilst at other times they can take twice as long as the estimated delivery time and you get worried about where the parcel is. They are kind of like a rollercoaster between good and bad in a way.

Person 1: When will my parcel arrive.
Person 2: Whenever Royal Mail delivers it.
Person 1: I've waited a week.
Person 2: I know Royal Fail can be like that sometimes.