But you don't have to draw the same characters over and over all day long for years either. ;)
I didn't say I understood it, but I've seen evidence of it. It's not too far removed from all the dirty jokes hidden in Who Framed Roger Rabbit, before Disney caught on, and erased them all.
It's probably on the same level as office humor. My father and his co workers used to circulate dirty jokes and cartoons in the era of xerox machines and faxes. It would be very un-PC today of course.
My classmates back in college at the tv studio pulled all manner of questionable jokes, some of which made it to air.