Well this is like Lord Voldemort in Harry Potter, who is simply referred to as “He who must not be named” lately people have been experiencing a crazy bug on OS X, when they type in a certain phrase.
According to a copy of the bug on Open Radar, all you have to do is type the text below into almost any window in any app on OS X to immediately crash the app. In order to prevent crashes on our and your end we have added the text as an image instead. All you have to do to recreate the bug is type the text below into almost all OS X apps, it is important that you make sure your F is capital and that you add all three slashes for this to work. The bug affects all Macs running Mountain Lion, but it does not have any effect on Lion or Snow Leopard.
So far we have crashed the Mail app, Tweetbot, Notes, Safari and TextEdit with this odd bug, it seems however that some apps are immune to the bug, but we will leave it to you guys to figure out which ones are.