Latrinalia is probably the form of graffiti that we are most familiar with, yet we don't really like to think about it.  What someone writes while they are taking a crap isn't necessarily considered literature.  There is a reason that bathroom graffiti is so unadulterated; the anonymity of the situation makes it much easier for someone to write dirty things on the wall.
    German graffitiologist (bet you didn't know there was such a thing!) Hugo Luedecke states that there are two types of bathroom writers: the intellectuals, who write their messages in poetry, and the commoners, who write in prose.  There is a lot of Freudian interpretation that can be applied to latrinalia which seems quite preposterous.  Some scientists think that when a person enters a bathroom stall, he becomes excited by the smell of human waste to the point where he becomes inspired and therefore becomes capable of putting those thoughts into verse.  For example:

        This is by no means literature, but if those scientists are right about the smell of waste stimulating the human brain, we might want to consider doing some more productive and creative activities in the bathroom.

    Despite the fact that women and men are now "equal," it is men who are the predominant bathroom writers.  Women aren't completely innocent, though.

"Women unite! Men have long dominated the bathroom graffiti scene- Rise up and fight oppression with our imaginations!"   -(U.C. Berkeley)