An individual whom is concerned with the exact particulars of every topic being discussed. Will let third party know when they are incorrect about any and every topic, even if the topic in question is minor or unimportant.
Third Party: "Bill and me went to the lake to fish, and it must have been about late September"
Exactologist: "Actually your wrong it was September 15th, so more like mid September."
Someone who has mastered the skill of ermatology to a professional level, either through years of study or personal experience.
Steve: Wanna hang out tomorrow?
Dave: Can't, I've got an appointment with the ermatologist.
Steve: No problem, everything okay?
Dave: Yeah, I just accidentally used the word "effect" instead of "affect" and he said he wants to see me as soon as possible just to make sure it's not a symptom of something more severe.