Stimpy has sex with a duck to the point where an egg comes out of his anus.

adult

One episode features plenty of female nudity, and other episodes have nudity but not as much. The show hints that Ren and Stimpy are gay and there is an episode where Stimpy is pregnant. (he is actually constipated)

Very frequent innuendo.

Full of shocking brutal violence. Blood is often included.

One episode shows Ren torturing small animals. Later in that episode, he kills Mr. Horse, bites the hand of a dog catcher, and a frog shoots itself in the head.

Occasional occurrences of "Fuck", plus frequent uses of milder profanity, including shit, bitch, bastard, crap, hell, piss (or pissed), pussy, and damn.

Ren tends to smoke a lot and drink beer, but this happened sometimes in old cartoons.

The whole series in this Ren and Stimpy spin-off for adults only is disturbing and psychotic.