Why do some people behave so abominably at parties, and what is your worst party experience?

I went to a very elaborate party, over 700 people, in a huge house for a political cause, and the guests stole several things, left incredible damage, cigarette burns in the furniture and the carpets, damaged valuable paintings and generally behaved like rabid baboons. So unfortunately some people are just out of control and behave very badly at parties, but the most personally embarring was a friend of mine got very drunk at a party of an actor friend of ours, and Anthony Hopkins was there, (YEARS before Hannibal) and she had a crush on him and while I was talking to him she came up to him, weaving, eyes gly, hair all over the place and asked him a gazillion questions and unable to focus her eyes and while this was going on she went over backwards and ped out cold for a while. I was so embarred I left with someone else.