"the absolute worst shopping experience I can think of"

Indeed:

* Short opening hours

* checking the membership card at the entrance

* cell phone salesmen inside

* item locations change randomly

* items randomly disappear for weeks at a time, as if Leonid Brezhnev was in charge of restocking

* waiting at the exit for someone to check your receipt

* for a while, they'd check your receipt at the self-checkout and then check it again at the exit

* 1970s level IT, inaccurate inventory information

Microsoft used to give a cash bonus for patents; I imagine Costco has a bonus program for new ideas to make the shopping experience worse. Some ideas:

* throw lit firecrackers into the crowd

* pour oil on the floor so people slip

* complete darkness inside the store

* every 10th person at the checkout has their credit card cut into pieces