Coincidentally enough, my darkest role was a co-starring one in "Bulletproof Monk." The original script had me playing the Seann William Scott role, but as a CGI monkfish made of kevlar. I am so method, I had to literally embody the characteristics of an ocean bottom-feeder (the darkest part of the sea where those fishes with headlamps linger).
Long story short, the studio balked when I kept referring to myself as Stifler in the voice-over room and they eventually retooled the script and cast the real Stifler as Chow Yun-Fat's sidekick. Needless to say, the movie bombed and Yun-Fat never worked in this town again.