It also prompted me to add a comment about the added risk for parents in the USA. As you may know, kids can't legally drink until they are 21 here. Not only can they not drink till 21, even when they are 21, if they let their friends have a swig, it constitutes supplying a minor with alcohol. I tell you, college is a bloody nightmare these days. They all seem to drink anyway, and every college seems to have a different way of handling it. It's rarely dealt with by the "real" police so a lot of them aren't prosecuted, but it doesn't mean it doesn't have an impact.
Some colleges give you a one-time pass so it doesn't count as a discipline matter and doesn't go on your record. Students are usually required to take some sort of alcohol-awareness course though, either on-line or bums in seats. Other colleges have the campus police haul the kid off to the local hospital where they have to sit and wait till they sober up. If the kid is really drunk, they might also be put on a drip to re-hydrate, resulting in (usually) a claim on the parent's health insurance and obviously, parents being thereby notified. A few colleges have a fairly strict approach and the student finds him or herself on a final notice; further infractions could lead to them being kicked out.
The people who could fare the worst though, are parents. Gone are the days where teens puking on your front lawn were a fairly regular occurrence. Many states now have "social hosting" laws, meaning that if under-age kids are found drinking in your house, you can be criminally prosecuted and/or sued by anyone whose child is endangered in any way. Oh yes.
And, depending on your state, that can apply when you have no idea your darling child has friends in the house 'cause you're not even in the same city! Even if you're at the party, provide booze for the grown-ups with strict instructions to all minors that they're not to touch it, should a teen drink it and then say, get into a car and injure someone else, you could well find yourself in deep doo-doo. The fact that you not only provided the alcohol, but "allowed" said minor to get into a car with alcohol in his or her system could also be negligence on your part.
Pity these poor parents in Maine, who had done everything they could to avoid underage drinking at their child's party, even going as far as asking local police to help screen guests. When it became obvious that there were lots of drunk kids anyway, the police got involved and the couple was indicted by a District Attorney who was pressing to have them serve jail time. Because the jury couldn't reach a verdict on this, the couple agreed to pay $17,000 in fines and restitution, write a letter of apology for the local newspaper and serve 100 hours of community service each. Apparently there was also very harsh criticism from local residents too. Yikes.
Hosting teen parties - a whole nuther matter in the USA.