(yawn) Charlie Sheen, again...
15 minutes before Tuesday's Sheen's Korner, the audio feed came on. It sounded like static at first -- but you can clearly hear Sheen rehearsing with his crew and Teleprompter. Near the end you'll also hear some last-minute editing as he decides how to skewer producer Chuck Lorre without sounding anti-Semitic. (more)
The point...
Always assume the mike is on.
One of the worst cases I witnessed was a corporate executive waiting to take the stage. He was wearing a wireless microphone and headed to the bathroom where he met another executive. Neither realized the mike was transmitting to the control booth; it was just not being pumped to the auditorium speakers yet. Some important guests in the control booth area heard every word. The conversation (not to mention the bodily noises) led to a very embarrassing public apology made during the man's speech.