Amen to this. I once had a professor who was a) a genius and b) insisted on editing code live during the middle of a demo after having found a bug. You could practically see the eyes of the demoees glaze over in real time.
Our other professor, who was a) a genius and b) had some marketing skill, approached every product demo like it was the invasion of Normandy. He didn't just have it drilled to perfection, he had a Camtasia video of the entire thing drilled to perfection so if anything crapped out he could say "Whoops, technical issue -- now switching to the video of when I did it earlier today. As you can see..."
I was at an international technical meeting where someone was about to show a web site on a projection screen. The browser's autocomplete tried to fill in the names of what were very clearly NSFW sites he had been visiting during off hours. It's easy to forget how much info your browser knows about you.
We once made a demo for our product in front of maybe a hundred people and everything went wrong. Our live system was down, our backup system was not working and we didn't have the right codecs for the videos. Sometimes the Gods of demo don't want you to demo your product.
Just another tip, create a demo user on your computer with all the stuff ready on the desktop (links, images, videos). It will more professional.
And clear out test data and files. I once did a demo and stumbled upon a page that had a file called "vida-guerra-nude02.jpg" or something like that. Ugh. I closed the page fast but probably not fast enough.
Our other professor, who was a) a genius and b) had some marketing skill, approached every product demo like it was the invasion of Normandy. He didn't just have it drilled to perfection, he had a Camtasia video of the entire thing drilled to perfection so if anything crapped out he could say "Whoops, technical issue -- now switching to the video of when I did it earlier today. As you can see..."