For me it was in the men's washroom.  The first time I used a regular urinal and my penis hit the bottom of it.  I screamed like a girl and everyone stared.

Now I only use the "child" urinals, which are a foot lower to the ground - see link below.  

(In case you are wondering, at home I stand on a stool over the toilet so I don't hit the water)

http://www.jamesrobertwatson.com/images/urinal1.jpg