rm

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".