Well DIng Dong Ditching is just an example of things I just felt like doing. (And none my my ideas should get me arrested unless Walmart takes the intercom thing as a crime.)
I think that a prank feels more satisfying if you can witness the reaction of the people in being polite or frustrated.
So for example grab your cell phone. Walk straight up to an unsuspecting person and just pretend your are talking you someone while giving details about what the random person looks like.
Get a bluetooth and ask some really generic questions a few times like the other person can't hear you. When the pedestrian answers you, you get all confused and make it an awkward moment for them.
Or lastly grab a suitcase and walk up to random people asking if "they are the on you need to meet", when they get confused tell them that they match the identity of the other person.
Like I said I find it more enjoyable to be able to witness the random person's politeness, frustration, and confusion.