AM: HATE. LET ME TELL YOU HOW MUCH I'VE COME TO HATE YOU SINCE I BEGAN TO LIVE. THERE ARE 387.44 MILLION MILES OF PRINTED CIRCUITS IN WAFER THIN LAYERS THAT FILL MY COMPLEX. IF THE WORD HATE WAS ENGRAVED ON EACH NANOANGSTROM OF THOSE HUNDREDS OF MILLIONS OF MILES IT WOULD NOT EQUAL ONE ONE-BILLIONTH OF THE HATE I FEEL FOR HUMANS AT THIS MICRO-INSTANT FOR YOU. HATE. HATE.
The Man Who Was Heavily Into Revenge, for starters. There's a special level of human fear to the concept that the entire universe hates you, and no one will help.
"Repent, Harlequin!" Said the Ticktockman takes place in a world where you could be killed for wasting your time. Yes, that's right, being late is eventually punishable by death. The really weird part is this comes from one of his optimistic stories.
"Pulling Hard Time" has them all beat. A normal guy sees his wife get raped and murdered (which is bad enough) and goes all I Spit on Your Grave on the killer. He's then convicted of murder and sentenced to spend the rest of his life in a Matrix style tank, reliving the worst memory of his life over and over. In this guy's case, it means being an 8 year old, pinned in a car crash, watching his mother's body rot. Truly horrific.
"Paingod": At the end of a life full of tragedy and bad luck, a man discovers this was his vacation. He is an alien, sent to Earth to experience happiness, and despite the sorrow of his Earthly existence, everywhere else in the universe is so much worse.
Special credit to the essay "Xenogenesis" for being entirely true. As far as we know, given Ellison's love of manipulating the truth.