I'm not surprised you got them to laugh....what did you do now.... : )
I find it odd that doctors/nurses either are surprised or are in disbelief when we tell them our blood types (I'm AB+) (and I even know my daughters': one is A+ the other A-).
Blood type is info most people don't know.
My brother and I had to know ours growing up as were were often bleeding and bruised due to our misadventures.