Is there a toy more simple (or annoying) than the Clackers? Popular during the 60s and 70s, Clackers were two hard plastic balls about two inches in diameter that were attached to a tab by sturdy string. While holding the tab and making an up-and-down motion, the balls swung apart and came back together, striking each other and making a clacking sound.
Clackers were similar to the Argentinian weapon called bolas. In the 19th century, these bolas were used to frighten birds away.
As you can probably guess from the description or your own personal experience, Clackers posed a safety hazard as children often injured themselves. In addition, the force at which the balls struck each other sometimes caused the balls to shatter.
Clackers have made minor revivals in popularity with less hard plastic balls.