Zell spurts out random gibberish that seemingly no one understands, this lack of communication leads everyone to believing he is an nonsensical idiot which frustrates him.  Ideally I'd like Zell's accent to be something that is stereotypically difficult to understand such as British cockney, gutturalScottish or any accent really that speaks with rapid succession.  Try to find a balance between getting the lines across but with a ridiculous tone/accent.