Level I:
Your guests are conversing quietly, nibbling at their hors d'oerves, and sipping their drinks. Later, some of the gather by the piano to sing carols while others admire the ornaments on your tree.
Level II:
Your guests are talking loudly, wolfing hors d'oerves, and drinking from the bottles. Some people gather by the piano to sing "I Gotta Be Me" while others begin rearranging your ornaments.
Level III:
Your guests are arguing wildly among themselves, those that haven't passed out from the upside-down margaritas. One person is singing "I Can't Get No Satisfaction", which can barely be heard over the sound of breaking ornaments. A small group of guests begin placing hors d'oerves in the piano to see what happens when the little hammers strike.
Level IV:
Your guests, hors d'oerves smeared over their naked bodies, are performing a ritualistic dance around the burning Christmas tree. The piano is missing.
In general, you want to keep your party around Level III, unless you rent your home, have insurance, and are carrying firearms. The quickest way to get to Level III is egg-nog.