4. Jeffrey Dahmer
Jeffrey Dahmer definitely earned his sterling reputation as one of the sickest serial killers of all time. Over a 13-year span, from 1978 through 1991, the Wisconsin-born freakshow killed 17 men, but when we say "kill," we really mean that he ended their lives via rape and dismemberment and then prolonged his sadistic enjoyment after their demises by having sex with corpses and eating some of their flesh.
Dahmer was a sexual predator, meeting guys at local gay bars, flirting with them, and having sex with them before his real "pleasures" would begin. Late into his murder spree, Dahmer thought that he could turn people into "zombies," so he started drilling holes into his still-living victims' skulls and injecting hydrochloric acid into their brains' frontal lobes, hoping to turn them into docile, submissive sex slaves.
In the end, Dahmer received his comeuppance in prison, where another inmate beat him to death in November 1994.