These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Family Unfriendly Aesop: The ending of the movie. Fritz concludes that he should stick to having sex with everyone he can and let the world take care of itself.
Sequelitis: The Nine Lives Of Fritz The Cat was written and directed by Robert Taylor, without the involvement of Ralph Bakshi or R. Crumb. However, producer Steve Krantz and actor Skip Hinnant worked on both films.
This Is Your Premise On Drugs: Subverted. Oddly enough, even though Fritz is shown more directly partaking in drug use, the comic is far less surreal than Felix The Cat.
What Do You Mean, It's Not for Kids?: The comic is an early example, although Crumb's graphic novel Oggie and the Beanstalk was more directly an example of this, as it was mistakenly stocked as a children's book by some stores early on in its distribution. Some distributors confused the film and its sequel for children's films. Supposedly, the sequel was even aired on Showtime Family, despite its X rating.
Alternatively, the Showtime Family claim may have been made by a Troll. You can't take everything stated in IMDb reviews seriously.
Although, with Tag Lines such as "We're not X-rated for nothing, baby!" and "He's Animated and X-rated!", there's really no excuse for thinking it's for kids.