Here are a few; please add more (:





Change the viewfinder focus.





While the photographer is walking see if you can detach the lens from their body without them noticing. Run. Bonus if you can get their eye cup too.





When they put the camera up to their eye always put your hand in front of the lens, when they put the camera down remove your hand; rinse and repeat.





If their lens cap is on shout as loud as you can "YOUR LENS CAP IS ON!"