Designated Villains: Hector, Wordsworth, and Mungo whenever they appear in the Heathcliff segments.
Ear Worm: The doo-wop style theme tune is quite insidiously catchy.
Ensemble Darkhorse: The Catillac Cats. When this show aired, it was always about Heathcliff. Only his segments were acknowledged in promos and commercial bumpers (the ones by Fox Family). However, most fans of this show will agree that The Catillac Cats series was much better than Heathcliff's.
Maybe not being based on an established, but very dated comic book property had something to do with that.
Germans Love David Hasselhoff: The French have the entire show on DVD because of that. Also, there were some toy figurines of The Catillac Cats produced in France. Even a toy Cadillac car that could be changed into a hovercraft, and trailer, just like in the show. If you're lucky enough you can find these up for auction on eBay.
It helps that the show was partially made in France.
Dixie (the athletic cat whom Mungo falls for) in the episode "The Games of Love" looks very similar to Minerva Mink who wouldn't exist for another nine years.
The Catillac Cats episode "Time Warped", almost feels like a parody to Back to the Future Part III, what with the cats sent back in time to the old west, the Cadillac filling in as the De Lorean, and having to use a train to get back to the present time. However the episode was made at least three years before BTTF III hit theaters.
What Do You Mean, It's for Kids?: Watch the Catillac Cats segment "Kitten Around", and do a shot every time you notice something that shouldn't be shown to a small child. You'll either be dead or passed out drunk in less than ten minutes (five if you're a lightweight).
The main topic is Riff-Raff wanting to go steady with Cleo. The main rule: No other guys for Cleo, no other girls for Riff-Raff.
They even have a 'boing' sound effect when Cleo kisses Riff-Raff after saying she would go steady with him.
Chuck Lorre co-developed and wrote for the series (even though he now considers this an Old Shame and doesn't really like cartoons in general). Perhaps this was one of his "contributions".