To me the canonical example of this is meh.com. They offer one product per day, and each day there is a “meh” button. You log in, click the button, it spins and

To me the canonical example of this is meh.com. They offer one product per day, and each day there is a “meh” button. You log in, click the button, it spins and reveals a custom “meh” face tailored to the thing on offer that day. You can only click it that day —- it changes each day, no historical option —- and on the home page it shows how many days in a row you have clicked it. On your account page it shows all the ones you have clicked. The button does nothing: no discount, no deal, nothing. And yet at the end of Meh’s first year they issued a report and said that something like seventeen people had clicked that button every day of that year. That kind of habit is huge for a site like meh.com, and they accomplished it with a silly button that does nothing but show a custom illustration.