I did something similar this year for April Fools. An "Enter Admin Panel" link mysteriously appeared at the top of the forum, luring unsuspecting members inside. It looks and interacts just like any normal, functional vBulletin ACP, of course all the important functions are disabled, though. All the menus are collapsed by default, except for one which contains a bolded link "Prune all Posts/Threads" - and each time the User clicked this, they got written to a "Naughty List" that was put up the day after April Fools.