I had this kind of discussion on a another board and I came to this conclusion: it is pretty arrogant to proclaim yourself an "expert". This would imply you know it all or most of what there is to know. Biology is never black and white so what you think you know one day might not be right the next.
I think it is easier to be called "expert" by someone else but I think it's funny when someone calls themself an expert.
I don't think there is such a thing as an "Expert" but there are some people who know more or are "luckier" than others.