What does Rietadt mean?

For the contest he went for a rietadt instead of a normal chug.

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

For advanced drinkers, a rietadt (also called rietbak) goes faster than a normal adtje. The straw lets air in and the drink flows fast. It is a lot like chugging, with a little help. Also read about adten and riet.