The year is between 2000 to present. I'm trying to find a movie (I think it's foreign). I just remember bits and pieces. Husband and wife are on the beach and a bunch of rowdy kids are blasting their radio. The couple ask them to turn it down. Everything gets out of hand. I remember them stealing their car, kidnapping her husband and killing him. She kills them one by one. At the end she enters one of the kids home, and the parents discover she was killing their kids. She locks herself in the bathroom and they're trying to get her out. Thanks.

That's definitely Eden Lake (http://www.imdb.com/title/tt1020530/).

Fantastic yet very brutal film.