A cute puppy looking for a handout gets backhanded by a crabby, stingy lout. The lout starts chewing on and peeling back a hangnail. The pissed off puppy “helps” his master with the hangnail and exacts some painful skin-flailing revenge in the process. The guess here is that director Shane Acker has seen every single “Ren and Stimpy” episode ever made. With these characters enduring the likes of icky bulging eyeballs and having their peeling flesh turned into raw meat, “The Hangnail” shamelessly apes the squirm-inducing visuals of those early John Kricfalusi Ren & Stimpy classics, the first cartoons to make the grotesque acceptable. “The Hangnail” spends nearly all of its two minutes on the set-up, giving the viewer plenty of time to brace himself for its painfully graphic but disgustingly funny denouement. It doesn’t even pretend to be subtle, which is why is why you’ll see it soon as part of the newest edition of the “Spike & Mike’s Sick & Twisted” animation fest.