At one point in "Big Baby Scam", Old Man Hunger (the crazy, naked guy with the chicken drumstick on his head) takes a bath with Ren and Stimpy and starts whistling "In The Hall of the Mountain King." This is the Leitmotif of Peter Lorre's character in the movie M — a pedophilic serial killer.
Fridge Brilliance: That scene is one of many to be edited in reruns on television. Maybe someone in the S&P department discovered this or already knew it in some capacity.
Stimpy frequently touts the edibility of Gritty Kitty litter (he and Ren even consume it on-camera). In real life, cats do eat litter, but only if they're ill or suffering from a vitamin deficiency.
"Space Madness". As a kid, it didn't seem too bad, but think about the scenario as an adult: Ren and Stimpy are both astronauts who haven't seen Earth in (presumably) years, who are the only ones on their ship, who don't eat real food (instead, they eat pills), and who have six years of free time on a ship where they have nothing to do but stare at each other. Is it really any wonder why Ren snapped?
Sven Hoek is introduced as Ren's cousin. However, Ren remarks that they were littermates and shares a photo of the two as newborn puppies. If they were littermates, they were born of the same mother, but as cousins, their parents were siblings. In other words, Ren and Sven were the product of brother-sister incest.
In the episode "Sven Höek", Ren becomes angry for Stimpy and Sven ruining his most prized possessions. One of these things is a collection of rare, incurable diseases in jars. Jars that have been opened. Letting the diseases out.