Lionel Dahmer tells son Jeff that psychopath Ed Gein (1906-84) killed a lot of people. While Gein was suspected of 9 total murders, only 2 were ever confirmed.
Lionel mentions Ed Gein who reportedly inspired the Norman Bates character in Psycho (1960), Buffalo Bill in The Silence of the Lambs (1991), Leatherface in The Texas Chain Saw Massacre (1974), etc.
As Dahmers mother walks into her office in the early part of the show she is greeted by the receptionist in an uncredited role played by Trevor Snarr.
Trevor Snarr played the role of Don Moser who is the bully/boyfriend of Summer from the film Napoleon Dynamite.
If you look closely he makes the distinctive eyebrow raise that he did in Napoleon Dynamite to Dahmers mother as she walks past.
Lets call this an Easter Egg.