To install the prank, first select the one you want to use (explosion, which is the one in the video below, looks quite interesting) and somehow get the phone away from your friend. Because this is merely an interactive website, no Apple ID is required. Create a homepage bookmark, launch it from Springboard, press the lock button and you are all set.
When you do pull off the gag, you best reveal it to be a joke quickly before your buddy does some bodily harm to himself.
source: iPhoneception via TUAW