FakeWhale

Just launched at Atlanta Startup Weekend, this ATL-based site lets you create fake tweets from your friends'/enemies' accounts by mocking up a Twitter-looking page with your target's handle and picture, which you can re-tweet to make it look like they actually posted...anything. They make it plain that any fake is "purely satire, so don't take it too seriously", but when you're posting as IAmDiddy, that's clearly impossible.