Funnily enough, I just watched TIny Toon Adventures Spring Break Special, and parodies of both duos appear near the end, both chiding and dismissing the Tiny Toons before being ran over by the Tiny Toons' bus. The parody of Beavis and Butthead had also appeared earlier in the episode, but when they made their appearance alongside the Ren And Stimpy lookalikes, they are called a "disgusting excuse for a cartoon" by the Ren parody. Perhaps this was a potshot that was referring to John K's noted opinions on animation, or maybe was it just the amount of controversy that B&B had amounted at that point?