It seemed pretty obvious to me when I first heard about the site. No matter what level of intelligence a body has, no matter what a fine upstanding citizen they may be, anyone that uses twitter is a twit. Not a tweeter (site isn't called tweeter) & not a twitterer (which isn't actually a word) but a twit.
Kinda locked on the word when twitter exploded in the news, late 2008. The President was addressing Congress and a disturbing number of those assembled weren't paying attention to him but tweeting instead.
Nothing wrong with being a twit, that bad example aside.
Resisted for the longest time but eventually I caved and I've actually had a pretty good time with it ever since. Don't have the best gear to tweet with but I do what I can.