You know of Fake Sarah Palin by now, but one order higher on the complexity scale of humor is interaction between fake celebrity Twitter accounts.
@michael_bay has a saying: "I turn things from boring to awesome. Then I turn them from awesome to Bay."
My favorite fake Michael Bay tweet:
If Im groggy in the am I get a triple venti espresso from starbucks and dump it on the first homeless person I see in downtown LA. It works.
Every character on Mad Men seems to have their own Twitter accounts, though they don't quite do it for me. Part of the charm of those characters is their entrenchment in that time and the inscrutability of their inner lives, so the self-conscious and reflective nature of a Twitter account doesn't fit (AMC briefly had Twitter take them down, though they've since been restored).