A term used to describe that one person in the office who in any given situation, be it a large meeting, small meeting, or casual conversation simply will not shup up. This person seldom stops talking so that they can be the center of attention and voice their opinions about everything possible.
When speaking to this person you may believe them to be listening. However they are not hearing a single word you say and are instead trying to find the first entry point for them to interrupt you and resume talking.
A wont-shutup-a-saurus will often tie up others in the office for large periods of time with total disregard for the fact that they may have work to do or that there may be a person waiting to talk to them about something important (even if this person is standing directly behind them).
Boy that guy sure is a wont-shutup-a-saurus, he was talking to me about his ridiculously over priced suit & shoes for over an hour yesterday.