Most Embarrassing Presentation

What is the Most Embarrassing Thing that has Ever Happened to You or Someone Else in a Presentation?

We've all had those hiccups in presentation delivery where we either just freeze, or visual aid malfunctions, or we prepare an hour-long speech and are told just before we start that our available time has dropped to 25 minutes. These glitches can cause embarrassment, but they are also fantastic opportunities to shine. What was your most embarrassing presentation moment, and if you recovered... how did you do it?