Two leaders, a chair and volunteer, and a plastic or Styrofoam cup full to the brim with water.
Get a volunteer and lead them into another room. While they are away clue in everyone else what is going on. Basically the scene is a restaurant the youth leader is the customer, the other leader the waiter. The volunteer must be the table. Lead the volunteer in explain to him that he or she is a table. They must act like a table, rigid and supportive, strong and straight. Get them set up as the table with the chair beside them. Now the youth leader walks in and the waiter comes up to him and asks him for his order. Act this out in as funny a way as possible. Then the waiter asks what the customer would like to drink. "Oh, just water" The waiter leaves and returns with the Styrofoam cup of water which either he or the youth leader places on the table right between the victims shoulder blades. then everyone runs away. It is impossible to get the cup of your shoulders without spilling the water all over yourself! But it is fun watching people try!