@Harp That one kind of makes me snicker. I know of one who has that listed who, from my observation, just might merit having it in there because they know a lot more about sex, sexual positions, sexual dynamics, etc. than the average Joe/Jane. However, that is one member.
Oh, I do not even list “martial arts” in my expert list because, while I have blackbelts in two arts and have been practicing for decades, I do not know as much as many… I know my styles, body mechanics of the martial arts, and the like. There is one member here that I know, with absolute certainty, who knows 10 times more than I, knowing the history of the martial arts… period. He has been in the arts longer than I have and dedicated his entire life to his study, just like I have with my study of the Holocaust.
I guess that is part of my criteria for expert: the time and passion with which you study and learn. I have been studying the Holocaust since my teens (I am 47) due to needing to understand why my people and family were slaughtered in it (I am not a Jew). This includes all peripheral study needed, such as sociology, psychology, and more.
The guy I describe has done the same with the martial arts. I know a number of people who have done what he has, actually. I have not which is why I do not list it. I know my specific styles, general history of the arts, and philosophy of the arts.
My study into such as the Holocaust, the history and present situation of my people, etc. is a consuming one. I never stop… ever. I have lots more to learn and am going to learn it.