Presentation Mistakes: The View From the Audience

I routinely do presentations and thought many of the things I do and know about presenting to an audience were simply common sense.
However, sitting in workshops over a three-day conference gave me the perspective of a participant. It appears that many of the common sense things that I do and know are not so common sense.
How many ways can someone screw up a presentation?
From the back row, let me count the ways!