The Disney animators made an underground Mickey Mourse "pr0n" cartoon in the 30s (? I'm guessing from it's being in B&W and the style of drawing). A print actually made it to the Brattle Theater in Harvard Square where I saw it in the 70s. It was pretty mild though...mostly it lampooned the Mouse Factory.
I remeber seeing some 30s porn animation years ago. Actually, it was quite humorous--not something I would want a kid to see though. Bety Boop herself was supposed to be a hooker. There was one where the character was supposed to be gay. They had this foppish guy swishing around and all the flowers were swishing around--it was hilarious (risque but not actually porn--but you got the message).