In public, while casually walking towards a group of people who are also walking towards you, as you get to about ten feet away from them, put on a face of absolute terror (exaggerate your expression), do an about face and run as fast as you possibly can. Exclaim something out of fear as you turn (ex: "OH stuff.") Bonus points if people start to run with you.
When you get into a crowded elevator, face AWAY from the door so that you face everyone else in the elevator. Bonus points if you get everyone to awkwardly look at the walls or floor.
Stare at someone across a room, even if they're not looking at you. When they do... keep staring. Bonus points if they leave whatever room they're in.
At the store, buy the cheapest thing you can find (like a pack of gum or even a small bag of chips) and pay with a $50 bill.
Give a homeless person a coupon instead of money. Bonus points if you put the coupon in your wallet to make them think they're getting an actual bill.
Set your ringtone to rickroll. If your phone rings in a crowded, quiet place, don't answer it.
Go to a public place that has a restroom only one person can enter at a time. When you know it's not occupied, wait outside. Bonus points if you form a line of at least five people. Double bonus if you form a line of at least ten and then have a friend casually walk in to the vacant restroom.
In the men's restroom, look for two men occupying two urinals and use the one in between them.
In a quiet room (like a library or a classroom in the middle of an important test), cough and sniff at regular intervals.
Make hideous faces at children while their parents aren't looking.
Stare at person's forehead instead of their eyes when they talk to you, occasionally glancing back at their eyes. Extremely fast way to make them feel insecure.
Go to a christian and tell em "Satan loves You" Works every time.
Wear surgical masks and gloves everywhere and act like you normally do, as if you weren't wearing them. It will scare the stuff out of everyone, especially if a lot of people are getting the flu in your area.
Go to Burger King and order a big mac
When talking to someone and another person walks up, start shushing each other and say "here he/she comes" loudly enough for the approaching person to barely hear.
While walking, swing your left arm with your left leg and your right arm with your right leg. As people watch you walk, they'll notice something is off but not know what the forget it is.
When invited to go to a friend of a friend's house who you know you will never talk to again, right before you leave, take a massive stuff in their bathroom and just leave it.