A good few years back I was supposed to go to a meeting in Hampshire which got changed to a meeting in London which I couldn't then get to so agreed to dial into alongside a few other remote attendees, whilst everyone else sat round a table with the audio coming out of the ceiling speakers. I couldn't find a meeting room/quiet office where I was so dialled in on my Blackberry with wired earphones plugged in and listened.
About 30 minutes in, the PHB introduced the latest consultant who launched into his spiel about what a GENIUS he was and what changes he was going to make to how we managed comms (which was actually one of the few things that worked REALLY well on that programme, as we'd already hooked into all of the longstanding effective channels the company had and people looked at) and what BRILLIANT new tools he was going to introduce and how we would LEVERAGE these ASSETS to make a PARADIGM SHIFT (you get the idea, right? Dilbert would have had a field day).
No idea how this was being received in London but I had the Blackberry face down on my desk and my head in my hands, muttering "you ****ing idiot, what ****ing planet are you on?" or words to that effect.
The sounds from London stopped abruptly and a voice said "who said that? who's dialled into this call?"
At which point I spotted the microphone on the earphone cord which was still only a few inches away from my lips...
More recently I have typed a comment about a meeting attendee into the meeting chat window rather than the 1-2-1 chat window I had open with another attendee. Fortunately the offending person was so busy pontificating he wasn't looking at the chat. If he was, he's never mentioned it anyway.