When setting your Search Criteria, you can select which jobs you are willing to play. Currently, the party finder will show you party listings that include those jobs even if you cannot join due to [One Player Per Job] and your jobs all being in the party already.

Ostensibly, this will hide party listings based on the jobs you check in your Search Criteria, not the job that you currently have equipped. So if you select, e.g., WAR SGE RDM DNC and you are currently a DNC, it will hide [One Player Per Job] parties that already have (WAR SGE RDM DNC) but not parties that only have (WAR) (SGE) (RDM) (DNC) (WAR SGE) (WAR RDM) (WAR DNC) etc.