They happen, but I can't say I've ever been to one. We have large family gatherings for holidays (30-40 people in a 1500 sq ft house is semi-normal in my family), but that's not really a party and more a bunch of people sitting around talking and eating crappy food. I've been to plenty of smaller "parties" of ~10 people where we barbecue, play games, and sit around a fire until midnight talking, but nothing crazy.

Two houses down from the one I grew up in had a few wild house parties that had the cops called on them. The one I'm remembering had to have 50-100 people piled into that house and back/front yard. That's the closest to one I've ever been. Turned down a bunch of invites to them during college too.

But yeah, they're real. If you cut through the absolute insane sequences and all of the things with the cops, Superbad is actually a really accurate portrayal of a teenager in the mid-00s. From the party to the anxiety to the hopes and dreams of the kids. If you're looking for an accurate portrayal, you won't get much closer in my opinion.