the scene in Rescures Down Under, when the seagull is tied down to a bed, and gets stabbed repeatedly with shots by a demented doctor mouse creeped me out. I didnt like taking shots as a kid, and the seagull's complete and total fear, followed by repeated shots scared the crap out of me.
In Ren's Retirement, Ren thinks he's getting really old, and buys a coffin and decides to be buried and live down there. At the end of the episode, we see the inside of the coffin being like a mansion, with TV, jacuzzi, kitchen, etc. Then the doorbell rings. A giant insect with a Yogi-type voice and tie comes in. Seems harmless. then it fades to black. Afterwards, we see Ren & Stimpy, I cant remember if they were skeletons, or skin without insides. Either way, it was very disturbing to me.