In "A royal Family" Prince Joachim of Denmark tells this story about Margrethe: Once, at a state dinner, he sat next to her, and she taught him how to make small balls out of the bread they had with the meal, and shoot them into the other guests champagne glasses. Eventually she succeded in shooting one of the balls into Prince Henrik's glass, just as he was reaching out for it. Joachim thought he was to be blamed, but his father knew exatly who the sinner was, and that was what surprised Joachim most. That his father turned to her, and not him.
He doesn't say when this happend, but he has to be at least 18 years old to attend a state dinner. He turned 18 in 1987, so Margrethe was over 90 years old! She was indeed a lady with high spirit and fun to be with.