Cave art is a prehistoric graffiti made by horny teen boys

[Nowhere]

At least mostly, there's also some graffiti made by horny teen girls

Hmm...what they were doing in those caves...

http://dsc.discovery.com/news/briefs/20060327/caveart_arc.html

http://www.livescience.com/history/060214_cave_art.html

[lowlifecat]

so pr0n has been around for tens of thousands of years.

[TnT]

Dad: "Ugh-Ugh, stop drawing deers on the wall."
Mom: "You know what I found in his room today? Outlines of nude women!"