In this week's new video Mama arbeitet wieder, a construction company boss tells his foreman:
Aber bevor wir hier abziehen, lassen wir's noch mal richtig krachen, was?
But before we pull out here, we'll make a really big noise [celebrate], right?
Caption 4, Spielfilm: Mama arbeitet wieder
The verb krachen is defined by the Duden dictionary as primarily "einen Krach verursachen, auslösen" or "causing a loud noise." Its slang meanings are "to have a fight with somebody" (Krach haben) or "to suffer a bankruptcy" (Krach erleiden), the latter similar to the "crash" of the stock market in English. The verb combination krachen lassen, however, usually means "to celebrate."
Da wünsche ich euch viel Spaß! Lasst es krachen!
Then I hope you have a lot of fun! Make some noise [celebrate]!
Caption 70, Silvester und Vorsätze für das Neue Jahr
A variation to the translation "to celebrate" is made in the case where a car really "makes some noise":
Und die lassen es in der brandneuen, über zweihundert PS starken A-Klasse so richtig krachen.
And they'll really, in the brand new over two hundred horsepower strong A-Class, make some noise [idiom: "cut loose"].
Captions 16-17, Mercedes Benz: Michael Schumacher und Nico Rosberg bei der Nationalmannschaft
So the slang term "krachen lassen" is usually used in connection with some kind of celebration, such as a birthday party or New Year's celebration. 2016 is still some months away, but that gives you a chance to get some practice celebrations going in the meantime. Lass es krachen!
Search for more videos on German Yabla that use the verb krachen and watch the entire video to improve your party vocabulary!