If you run Mac OS X Yosemite, don't use an emoji in your password
As at least one poor soul found out the hard way, there's a very good reason that Apple's latest OS X, El Capitan, doesn't let you use an emoji in your login password.
Apple doesn't have the same rule with OS X Yosemite. A user on Stack Exchange's Ask Different forum explained that he had used an emoji in his password on Yosemite — and then wasn't able to log in to his account. He originally posted about it back in August, but it's a PSA worth repeating.
When Artiom Dashisnky was creating his password, he'd used an emoji keyboard (on the login screen, you can hit "control+command+space" to get an emoji window), but the Yosemite login screen only supports native keyboards, making it impossible for him to sign in. He even had FileVault encryption enabled, which made it much more difficult to reset his password.
