"Declare as ennemy" does not complete the want "Make an ennemy"

FauvettEC​  Nope, they are 2 separate things.  You cannot declare another sim an enemy unless you have already made the sim an enemy and have a full negative (red) friendship.  A sim can be an enemy with only a partial negative friendship, but the option does not show up until the friendship bar is completely red.  The only place the Declare an Enemy comes into play really, is for 2 milestones in the Deviance>Public Enemy aspiration where you have to declare 1 and then 3 enemies.  

Hope this helps.