Here is my prank idea. It doesn't actually involve electricity (so it's actually safe). But it
looks like it does, so it could be scary to the victim of the prank.
Take a duplex receptacle that has been damaged in some way other than its front face (e.g. screws bent, etc) and is otherwise waste. Cut the plastic faces off. Sand the faces down to the depth of a duplex plate. Attach (glue) the plate and the two faces to a piece of black construction paper with the faces in the plate holes. Put some double side sticky tape on the back of the paper.
Now just stick the fake outlet up in a bathtub just before the inspector arrives
Another variation is to cut the prongs of an old plug short enough to stick into the fake outlet above. Then glue the plug on so it stays. Trim up the wires that come out from the plug so the conductors are exposed. Stick it up where people would see it.
