In what would you consider yourself an "expert"? Obviously, we are all Reds and baseball experts. We all know everything there is to know about baseball, so don't claim that. It can be anything, whether it is useful or not (just look at my list).
Here is my list:
-Latin (Spoken word or Written word)
-Coffee
-RPG/Zelda games
-The NBA
-Cheap Restaurants
-Channel Surfing
-Befriending foreigners (my friends list includes people from every continent in large quantities)