The Developers Ice Cream Cone is an item for Developers only, it will fire an ice cream cone that will do 200 - 600 damage. It is rumoured that it will be added to the game normally in 2.5 as a celebration for reaching that far, but that is not been discussed with the development team.
For developers, you spawn with the weapon, but if it is added to the game, it's damage will be reduced for normal players, but remain the same for developers. It will most likely be a Hard Mode item, and many people believe it will have something to do with the Hard Mode event, the Candy Moon.
If added to the game, the person who hinted at this said it will be called the Cream Clasher, making it sound much more dangerous than it may be. People reckon it may be a drop from the final boss, Sugarplum in the Candy Moon but it may also be crafted using end game items.