Optional: Alcohol of some kind
Blue food coloring
Put some blue food coloring into the orange juice punch until it turns a disgusting swamp-green color. The color is gross and the orange juice pulp floating around really adds to the effect. People will realize that the punch tastes good, but it will take them awhile to figure out it is orange juice.
optional: gummy worms
Freeze the liquid (and gummy worms if desired) in a clean rubber glove. Peel off the rubber glove and float the arm in the punch.