Who can't sue for patent nullity?
Bringing down an embarrassing patent

The French courts were able to rule that several of the patentee's competitors did not have a direct and personal interest in bringing an action to invalidate the patent in the main proceedings. Indeed, in order to bring an action in the main proceedings, a competitor must demonstrate the existence of a sufficient interest aimed at freeing up a forthcoming exploitation of the patented technique or a similar technique.

However, in the event of a main invalidity action brought by several competitors, the latter must demonstrate the existence of preparatory acts or serious plans...