I reckon that Roger from American Dad is based on Robert Downey Jr.’s portrayal of the psychotic child murderer Vivian Thompson in Neil Jordan’s In Dreams (1999).

Claire: YOU THINK YOU CAN SCARE ME, YOU SICK FUCK!
[crying]
Claire: Get out of my brain.

Vivian Thompson: I don’t like you anymore!
[points gun at Claire]
Claire: No, no. I don’t die here. I die in the lake, remember?
Vivian Thompson: Oh yeah.
[points the gun at Claire’s foot, instead]
Vivian Thompson: Maybe you develop a limp.