Literally a rock, in a box, with a straight-faced care manual — and one of the purest viral-fad case studies before "viral" was a word.
Pet Rock (1975) was a genuine nationwide craze decades before "going viral" was a phrase — and it's still made and sold today. This is a genuine pre-internet product — a real, nationwide sales phenomenon decades before social media existed, spread by nothing but word of mouth, in-store demonstration, and traditional advertising. Many of these are still in production today, largely unchanged.
Advertising executive Gary Dahl created the Pet Rock as a joke about the effort-free pet, packaged ordinary rocks in straw-lined boxes, and sold them for $3.95 each with a tongue-in-cheek instruction booklet.
The fad burned out almost as fast as it caught on — within about a year — but it's remembered as one of the clearest examples of a pure novelty-driven craze, and reproductions are still sold today as nostalgia gifts.