Instead of a smiley you could at least provide some info on that. This command will likely be destroying the current shell, as it displays the content of every regular file in the system, regardless of it being a text file or a binary one. And the first binary cat'ed to the terminal will crash the display.

But here's another nice one, giving you a complete list of all regular files on the system along with some meta data (size, modification time, owner):

This might be run as user as well as from a root shell. While run as normal user you will get a bunch of errors as you are not allowed to inspect some system files.