This is a famous lawsuit, Walt Disney sued a group of underground comic book artists/writers call Air Pirates for copyright and trademark infringements. The comics this group created featured Mickey Mouse and other famous cartoon characters doing nasty stuff, weird sex, drugs etc The defense was the comics were parody, therefore protected speech. The trial court disagreed as did the US Court of Appeals, the Supreme Court denied them an appeal to that court.
This was 1979, maybe there are other cases that followed that have precedent now.
http://en.wikipedia.org/wiki/Air_Pirates