His short, jerky actions mimic that of psychiatric patient in an asylum. Short babblings that lead nowhere, his super jumpiness, and the odd Jolly Rancher incident, all say "crazy". His movements recall more of Brad Pitt in 12 Monkeys than any other Lex Luthor from the past.
The philosophy that he explains and extols when referring to the painting on his wall, sound like the way Renfield refers to his master, glorious and dark.
And his dialog, ESPECIALLY his last portion of dialog, sounds like it was taken directly from Dracula.
Then there was this:
So, yeah.
Though I don't like him as Luthor.... as Renfield, he was pretty damn good.