Start with a plastic skull. Wash it well, and make sure that it's clean enough to eat off of. Because that's what you're going to do!
Congeal yourself some Jello in a big flat pan. Use only half the water the recipe calls for, because this way it'll be all nice and rubbery. Red flavors are best, but I used green one year when Meathead was a Vulcan. You want to get yourself a bunch of strips and patches about a quarter inch thick. Layer the Jello across the skull. This will make a nice interesting bottom layer for your guests to discover.
Similarly, take strips of cold cuts and layer them across the skull. I found a pound-and-a-half was plenty. You don't want to use too much, or else your guests won't eat their way down to the Jello surprise that's waiting for them! The Meathead illustrated is a ham meathead, which gives the appearance of a severe burn victim. You can also use corned beef, for the look of someone with the outer layer of his skin peeled off, or turkey for a nice zombie appearance. I used turkey the year that Meathead was Vulcan. You'll need to use strategically placed toothpicks to prevent the cold cuts from sliding off the head.
Next, add eyes. My personal favorite is pickled onions, for their pleasing translucency. The Meathead here uses the yolks of boiled eggs, for a nice jaundiced look, with pupils made from sliced olives. Cover the whole assembly with plastic wrap, and store in the fridge for party time. If you have housemates, be sure to warn them.
Finally, it's time for the magnificent midnight buffet! (Note: I always provide a barrage of food at midnight. If guests will be drinking, it's always good to get plenty of food in their stomachs. Late night food also makes them stay longer, giving time for drinks to start wearing off before they hit the road!) Remember to garnish Meathead...He looks ever so much better served on a bed of green leaf lettuce, don't you think?