Multiple complaint threads appeared on the forums after the 2006 Hallowe'en event, stating that they thought holiday emotes should only be unlockable once.
When unlocked in the 2008 Hallowe'en Event, it was called 'Terrified'.
You can run in the middle of the emote. If you do this, the game will act as if you are still doing the emote (i.e. "You are already doing an emote!")
Complaints arose after it was discovered that the emote was not unlockable after completing the 2011 Hallowe'en event. It was confirmed as a glitch, it as been fixed and is obtainable by talking to Frank outside the clan citadel portal.