Yay for DrBuffy.
See - I use 'I think' if I don't know, and just state the fact if I DO know (or at least, believe that I know, which may or may not be the same thing.) I also teach students to write papers that sound confident and knowledgeable - state facts, don't prevaricate.
What really drives me mad is when I say something very clearly, like 'put that there' (with pointing to the place) and someone says 'are you sure? did you think about?"
I tend to just stare at them until they finish, then repeat the exact instruction again, to make sure that they got the message.
Last time we moved house, 3 of the unpacking team were great, but there was another younger guy who kept asking a second time, or saying 'what about'. I ended up giving one or two word commands to him, e.g. "upstairs, bedroom 2" with NO attempt at politeness at all, until he got the message that yes, I did know exactly where I wanted my furniture in my house.
I'm really good at speaking clearly and meaning what I say without 'fluffiness'. Men are not always nearly as good at listening.