Here's a link to an acutal UK patent application for an adult advent calendar:

esp@cenet document view

Abstract of GB2328762

An advent calendar comprises 25 condoms each held behind a respective door for selective removal. Information is contained behind each door and a special condom is available on Christmas eve.

Not mentioned in the abstract, each day also provides a diagram of a suggested sexual position for the day. Unfortunately, the application seems to have been withdrawn.