Age
My kid and I were in a very crowded public restroom at a sporting arena, after looking to the man using the urinal to his right, my 6 year old son turns to address me on his left and exclaims, "Daddy, that man's wiener is a lot bigger than yours!"
The whole bathroom heard and looked immediately at me.
So I put my hand around my kid and told him "Well son, that's because daddy isn't aroused by men."