Mac: It's rare, but if you ever want to hide a user account from OS X's menu -- maybe for added security or to avoid confusing novice users -- this terminal command will do the trick.
In Yosemite, open Terminal and run the following command, replacing hiddenuser with the account you want to hide:
sudo dscl . create /Users/hiddenuser IsHidden 1
When you reboot, that hidden user won't show up as a choice. In older versions of OS X, you'll need a few extra steps, which you can find at the link below.