I show of a lot, especially when I'm a little drunk or something. Not just on a normal day, mostly when I have a party or when I'm going out with some friends.
Sometimes I get a semi-hard so it is absolutely huge, very funny to see the faces from friends or just people I don't know, although I'm straight.
Their isn't a special technique for showing off, it depends very much on the urinals, how much distance and whether there is a division or not.