Had a case a few years ago at my company where a message was sent to a couple hundred employees straight up, not BCC.
One person responded to all, asking to be removed from the list because they were no longer in the pertinent information chain.
Then other people started doing the same thing... then more people started calling out to people to stop replying all, and it just snowballed because a couple of people thought it would be funny to keep it going. I saw the same message send by the same couple of people several times.
It got so bad that it crashed the e-mail server (or they took it off line). That gave them a chance to clean everything out.
And it gave the group president a chance to issue a BLISTERING rebuke on the proper use of corporate e-mail services.
I heard through the grapevine (it's good being friends with group staff admins) that a number of people received formal letters of reprimand (which generally means you get an unsatisfactory annual review and don't get a raise that year) and, allegedly, two lost their jobs.