Something like this happened at my university a number of years ago. There was a side entrance that was ostensibly for usage by people with bikes (as it was par

Something like this happened at my university a number of years ago. There was a side entrance that was ostensibly for usage by people with bikes (as it was part of the bike storage area), but it was much more convenient than the main entrance and all you had to do to get access was ask at the security desk. So anyway basically everyone on this campus with 10k+ students and more staff had access to the side entrance. What everyone didn't know was that when you were granted access to this entrance, you were also added to the "bike storage mailing list". Long story short, at some point someone accidentally sent a message to the entire mailing list of ~100k people, which kicked off a long string off people reply-all'ing asking to be taken off said mailing list ("I don't even own a bike why am I on this mailing list"), which caused even more people to reply ("stop reply-all'ing for the love of god!"). I think there were 500 emails in my inbox from that by the end of the day.