Now, I work at a hosting company in the UK, as a linux support engineer. I've seen many cases where a number of clients ran one of the following:

rm -rf / something
rm -rf /var/cache (attempt to magento)
chmod 777 /var
chown -R user:user /*

Half the time, they're like "Hey guys, I dun did fuck up, please help!". The other half of the time, they piss me off. Here's a number of responses that really grinds my gears:

"Such a harmful command should really prompt for input before running" -- From the buy you "forced" a recursive rm command, which mutes such a feature.

Client: "I did no such thing"
Me: "I've seen the command history, and at the time the command was run, you were the only person logged in"
Client: "You're mistaken, You're reading the information wrong"
Me: "I assure you, I'm not, I know what I'm looking at"
Client: "Well you're a shit engineer"
Me (thought): "Says the fucker who doesn't know how to linux"

I like people who own up to fuck ups. But the ones that don't, are just making their lives harder, since we have all the evidence in front of us.

Most of these people are the developers, and in some cases, the sysadmins...