Matthew Keith bought his first Barbie dolls in the 1970s using his allowance money, hiding them from his parents for fear they would say the toys were not masculine enough. Today, 22 feet of bookshelves in his Los Angeles home are filled with his Barbie collection, worth around $20,000 (S$27,000). The middle school teacher's Instagram account, "DollsOnTheBrain," has more than...