What does Droog staan mean?

Because he had to drive that night, he decided to droog staan at the borrel.

Dutch student slang. This is a Dutch word. You will hear it a lot at Dutch universities, student associations and in student houses.

There is usually a practical reason to droog staan. Driving, work the next day or just a quiet night between parties without having to adten. At a Dutch student party you might need to explain it twice. But nobody really minds. Also read about sober and brak.