Yes - I AM talking about the Navigation address book - !!!
I haven't used the navi address book much, but this is what the DIS manual has to say:
Deleting a destination in a category except of Previous Destinations and Address List:
In the Navigation main menu, select the menu item Edit Addr. Book.
The Address Book editing menu appears.
In the Address Book editing menu, highlight one of the menu items Home, Work, Favorite Point 1, Favorite Point 2, Favorite Point 3 or Favorite Point 4.
Push the controller . The Options menu appears.
Showing the highlighted destination in the map
In the Options menu, select the menu item Show on Map.
In the Options menu, select the menu item Delete.
You will be prompted to confirm that you wish to delete the destination.
Select Yes or No.
The destination will be deleted or retained, depending on the answer selected.
From your original post, it looks like you may have tried this, however. I'll give it a shot when I'm in my car today and see how it works.