Step 1: Give the Victim a Hint
Tell the victim that you're going to the bathroom but secretly take a piece of chocolate with you.
Step 2: Waiting for It
Go to the bathroom and wait a while. Then flush and wash your hands. But before going take the Hershey Kiss or piece of chocolate a put some on you hand.
Step 3: The Hard Part
Now you have to go to the victim and ask for a high five. They will notice the poop on your hand (the chocolate) and tell you that you have poop on your hand. Then tell ewwww and wipe it on them. They'll start freaking out and just sit back and watch.