for those of you that don't want your kids to have parties and you know they might anyhow.
Bribe them. Promise parties but have them clean up and pay for all the alcohol/food/broken pieces of furniture/stains in the carpet. And be sure they'll be responsible about designated drivers and noise levels. Make them swear on their car, parent-paid credit card bills, next 3 months worth of spending money, or anything else you can get as collateral. Also make sure that they make it VERY clear that certain rooms are off limits. (Your bedroom, office, very nice dining room with plenty of breakable lladro). Lock those rooms if you don't trust your child's friends not to make out or peruse your belongings and possibly "help themselves". Also know when the parties are, people aren't allowed to stay for more than 1 night (in case they're drunk and no-one can drive them home). Make sure they follow the usual house rules such as smoke outside, recycle and throw away your stuff, wash the dishes. You might also want to make clear what is and isn't acceptable; accidentally knocking over a lamp and breaking it is okay, having people do drugs, even recreational, isn't.
This way if your child sees that it's okay to have a party but they have to be responsible about it, they can either go ahead and party or decide it's not worth it and keep the house off limits.
Forbidden things are ever so fun to young adults.
I've seen lots of people near my age (22) have parties since high school. Usually, the parent sanctioned ones are safer.
And then they'll be looking forward to the parties so they won't whine about you going to disneyworld.