Create a Bootable USB Flash Drive for Windows on MAC OS X

Download a Windows ISO from Microsoft website: https://www.microsoft.com/en-us/software-download/

As a precaution: it is recommended to remove any USB sticks from MAC and run: diskutil list
This will list all drives in your mac, plug now the usb and re run the command so you can see which driver path is assigned to your USB stick. In my case it was named: /dev/disk4

Now we need to unmount the USB:
diskutil unmountDisk /dev/disk4

Then:
sudo dd if=/Users/aidrissi/Downloads/Win8.1_English_x64.iso of=/dev/disk4 bs=1m

Eject by:
diskutil eject /dev/disk4