Party Jack

When someone prepares a party well in advance with a group of friends and another 'friend' suddenly creates another party the day before the original party with the same group of friends thereby 'Party Jacking' the original party.

Jill sets a Christmas party on Dec 20th a month in advance for her group of friends, sends invites, hires a DJ, etc and then a week before, Emily decides to throw a Christmas party on Dec 19th with the same group of friends thereby 'Party Jacking' Jill's party. Jill knows many of her friends will not show up to her party because they will be tired, hung over, not be able to get a baby sitter 2 nights in a row, etc, etc and is forced to cancel her party. Or if she does hold the party, it ends up being lame because few people show up due to already being partied out he night before.