As a server administrator, I rely mostly on root or sudo access--allowing me absolute control of the server. However, "with great power, comes great responsibility!"
You can easily accidentally do this devastatingly bad command of wiping your entire system clean.
rm -rf / # or rm -rf /*
Which looks almost identical to the popular command
rm -rf ./ # or rm -rf ./*
There was a recent prank on 4chan /b/ forum that, in short, instructed users to execute the above command in order to "unlock Apple OS X bitcoin mining".