I have an amazing memory for factoids (actually, for just about anything written), so my friends mostly treat me as a walking Wikipedia. My usual parlor trick is having someone go "Hey, Kendo, what's...?"
I also know a few others, like if you put your hand on top of your head, it can not be moved off by pushing up on your arm. I love teaching that one to small children, who will be lifted off the ground, or that the ring finger can not tap if the middle finger is pressed onto a table. I'm also a super-smeller, so I can tell scent profiles and ingredients very, very well.