For many the 1990s were the Age of Irony, with hipster cultural touchstones like Spy magazine and the TV show “Strangers With Candy” helping make snark the preferred flavor of the day. “The Simpsons” was also a big player in that area, yet arguably no cartoon series before had been quite so postmodern as “The Ren & Stimpy Show,” which premiered a couple years after it in 1991.