As far as monumental fuck ups go, this is probably near the top if you exclude ones that end up in people dying.
An unnamed man was doing his regular day to day job of operating the giant screen at the curiously named Maryland Stadium in Lanzhou, China when he clicked on an advert (most likely for porn) on QQ messenger (the big Chinese messenger service) which somehow resulted in pornographic adverts being broadcast all over one of the giant screens in the arena. Whoops.
The adverts were visible for a full 12 minutes before security spotted them and were able to get up to the control booth and shut them down. The worker was then published with a $500 fine and a 15 day stint in jail. Oof. Given what we know about Chinese jails, I’m not sure if the punishment fit the crime, but you can rest assured he won’t be doing it again in any case.