With how many new Linux users we get recently, I don't like this joke at all without a disclaimer. Yes yes, its your own fault if you execute commands without knowing what it does. But that should not punish someone by deleting every important personal file on the system.

In case any reader don't know, rm is a command to delete files and with the option rm -r everything recursively will be searched and deleted on the filesystem. Option -f (here bundled together as -rf) will never prompt for any non existing file. The / here means start from the root directory of you system, which in combination with the recursive option will search down everything, home folder included, and find every file. Normally this is protected todo, but the extra option --no-preserve-root makes sure this command is run with the root / path.

Haha I know its funny. Until someone loses data. Jokes like these are harmful in my opinion.