So that stuff doesn't happen at other get-togethers?

In this case there are no indications in any of the stories that there was any kind of trouble. And apparently none of the kids in this party back in 2002 were even over the alcohol limit for driving when tested, which is a fair way short of being fighting drink for most people. It sounds like it must have been a pretty restrained do.
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I'd have thought if you're old enough to get married or join the army without asking permission from your parents you should be old enough to buy a drink, but I gather that's not the case in the States.