Someone who spends a great deal of their time on micro blogging service, Twitter.
“Why are you spending so much of your time on Twitter? If you’re not careful, you’ll turn into a Twitterbug.”
A person who obsessively Twitters--that is, writes what they are doing every moment.
Person 1: Hey dude, what's up?
Person 2 (frantically): I have to Twitter this! You just asked me what was up! *Twitters that Person 1 just asked what was up.*
Person 1: Um, sure. I, um...have to go now. Bye! *innocently grins*
Person 2: *frantically Twitters that Person 1 is leaving*
Person 1: Wow, you're such a Twitterbug!