New Year's Eve Syndrome

The sudden inability of your friends to commit to attending your event or party out of fear that something better may come up that they wish to attend. This affliction presents most often around the New Years Eve holiday, where it gets its name, given the large number of competing parties to choose from.

"Are Bob and Susan coming tonight?"
"I don't know, they kept saying they weren't sure if they could make it."
"Sounds like New Year's Eve Syndrome; Mike decided today to throw a party tonight; they probably went there instead; a-holes."