Creating A Bootable USB Of Windows 8.1 On OS X?
I am not really sure why you would want to install Windows 8.1 without BootCamp.

The USB stick needs to be a little bigger than the .iso file you are going to be burning. It doesn't matter if there is any data on it, this will totally erase the whole thing.



Steps To Achieve Victory


Download the ISO you want to use
Open Terminal (in /Applications/Utilities)

2.1 Navigate to the path where the .iso file is located

2.2 Use ls to list all the folders 

2.3 cd /path/to/iso to dive in to folder or cd .. to go back the path  
Convert .iso to .img using hdiutil:
hdiutil convert -format UDRW -o /path/to/target.img /path/to/source.iso
Rename if OS X gave it a .dmg ending:
mv /path/to/target.img.dmg path/to/target.img
Type diskutil list to get a list of currently connected devices
Insert USB drive you want to use
Run diskutil list again to see what your USB stick gets assigned
eg - /dev/disk3
Run diskutil unmountDisk /dev/diskN (where N is the number assigned to your USB stick, in previous example it would be 3)
Run sudo dd if=/path/to/target.img of=/dev/diskN bs=1m (if you get an error, replace bs=1m with bs=1M
Run diskutil eject /dev/diskN and remove your USB stick
The USB stick will now be ready to use




IMPORTANT For the step #9 you can use the destination to /dev/rdiskN to reduce the copy time.

NOTE: Sometimes, not always, Step #4 will be necessary. Not all the time. I am not sure why it will add the .dmg ending and other times leave it alone.

NOTE 2: Might I suggest you learn the name of the .iso you downloaded, or just rename it win8.1.iso or something, and put it on your Desktop folder. That way, when you are typing commands like #3 and #4 etc, etc, you can type it like this:

hdiutil convert -format UDRW -o ~/Desktop/win8.1.img ~/Desktop/win8.1.iso


and 

mv ~/Desktop/win8.1.img.dmg ~/Desktop/win8.1.img


and step #9 would look like this:

sudo dd if=~/Desktop/win8.1.img of=/dev/diskN bs=1m




IMPORTANT - You can track the progress by pressing CTRL + T It will show the process info and records in and out, since we use the bs=1m each record is 1Mb in size so you can easily track the progress.



I don't mean to be insulting with Note and Note2, I am just making sure that you know what all these commands mean. It's the simplest method. Unless someone else comes up with something better.