People started flipping one cigarette upside down in their packs because of a myth that early 'Lucky Strikes' contained marijuana!
There’s a myth that people believed that the cigarette brand "Lucky Strike" is named so because every so often a consumer of the product would have a "lucky strike", finding a marijuana joint in a pack of cigarettes.
The myth varies in how often the marijuana cigarette would be included, anywhere from one in every thousand cartons to one in every pack. It's unknown when the myth originated. One claim is it has been floating around for many years. Lucky Strike's slogan "It's Toasted" fueled belief in the myth.
Despite the popularity of the myth, there are no reliable reports of any Lucky Strike cigarette containing marijuana. The name "Lucky Strike", in reality, is only a marketing ploy, implying to customers that obtaining their brand is a "Lucky Strike".
The "It's Toasted" slogan refers to the product's tobacco being toasted instead of sun-dried, making a supposedly better-tasting product. Other myths offshoot from this one.
One of the explanations for the origin of flipping a "lucky" cigarette upside down claims the practice originated from the Lucky Strike myth; it's thought that the superstition arose from flipping the marijuana-containing cigarette upside-down in order to save it for last.