Something that occurs when you are about to tweet. You look at the question "What are you doing?" and realize that the answer is truly nothing. And just before you type something insanely ridonkulous, Twitter Block makes you leave the computer or hit a toolbar key.
Fred: What are you doing?
Steve: I'm just staring at the screen. I want to twitter something but I've got nothing.
Fred: You've got Twitter Block, man. Just forget about it.