It's a romantic comedy for teens. It's one of the better ones I've read, though. So, there's some kissing(and more), talk about sex, and a strip club with strippers dressed like nuns. Also, there are a couple characters who regularly get drunk and hook up with whoever. Nick's band is underage but they play in a bar and drink alcohol. Don't forget the constant swearing, but its what kids hear at school every day.
I agree with what many others have said, that the book is not appropriate for some teens and teens who are not okay or used to the language/sex/drugs used throughout this book. However, in my opinion most of this stuff I see and hear every day at school. The language or inappropriateness was not a turn off for me, as it accurately depicts what things are like for most older teens.