AD IGNORANTUM

During a contentious discussion, my use of the phrase "ad hominem" to describe his behavior, caused an emotional response from the person to whom the remark was directed;  he countered with, "You see, that's what you do--use words that people don't understand."

Later, my ever-witty brother said, "You should have used ad ignorantum;  there probably wouldn't have been any doubt WHAT you meant."