One thing that often occurs to me when I see phallic graffiti is that it hasn't seemed to change much in thousands of years.

And yet, the male view of their own genitals in real life doesn't look much like most of the graffiti - the testicles don't sit at the side like two eggs bracketing a carrot on a table -- but that's one of the most common types I see scribbled here and there, and the one that comes to mind if one's cheeks are distended playing a straight pipe.