The act of throwing a huge party where the entire population of the city and surrounding area (200,000) are invited. Possers usually get broken up within 2 hours or less, and mass amounts of blood is shed. SWAT will be informed of a posser, and head to the posser house immediately. The owner of the posser house will usually go to jail.
Guy, were you at posser 06'?
Hey, I know you, I was at your posser last year!
No parents?!? Guy have a posser!