#3: Pretending you're pregnant. This will either get a lot of folks' hopes up, and dash them when you reveal the truth, frighten them at the thought you're breeding, or backfire horribly on you when you discover a month later that yes, you actually ARE pregnant.
#2: Pretending a store/game/sphere/business/place of recreation is closing. Not nice, people. Not nice at all. Unless you like seeing people start freaking out.
#1: Pretending you're dead. That one seems to be a real attention-grabber, especially on the gossip-fueled Internet. Lots of people will freak out, suffer severe doubts, freak out some more, weep and mourn and start planning the memorial, and then beat your sorry ass when you reveal the deception.
Why only three? Because frankly, I couldn't think of any other annoying AF pranks. I don't get out nearly enough. :> And yes, I saw examples of all three yesterday. :>