What is the official scale for grading Yak parties?

Festivity levels

Festivity Level 1: Your guests are chatting amiably with each other, admiring your Christmas-tree ornaments, singing carols around the upright piano, sipping at their drinks and nibbling hors d'oeuvres.

Festivity Level 2: Your guests are talking loudly -- sometimes to each other, and sometimes to nobody at all, rearranging your Christmas-tree ornaments, singing "I Gotta Be Me" around the upright piano, gulping their drinks and wolfing down hors d'oeuvres.

Festivity Level 3: Your guests are arguing violently with inanimate objects, singing "I can't get no satisfaction," gulping down other peoples' drinks, wolfing down Christmas tree ornaments and placing hors d'oeuvres in the upright piano to see what happens when the little hammers strike.

Festivity Level 4: Your guests, hors d'oeuvres smeared all over their naked bodies are performing a ritual dance around the burning Christmas tree. The piano is missing.

Most Yak parties never seem to go above a 3... a good party with lots of Pagans will reach Level 4 fairly quickly, however.