Mute

I was recently told about a conference call with half the universe on it, in a huge multinational, across four different time zones.  And in the middle of this call, everyone could suddenly hear the soothing tinkle tinkle of water, and the echo of what could only be the four walls of a bathroom.  It took everyone on the line about 5 seconds to register what it was and for the presenter to irritably say,

"Can we all go on mute, please?!"

And then I remembered a similar call where we were also talking across three million time zones, with twenty zillion heavyweights on the call and we could suddenly hear a dog barking and someone scream at the top of their lungs,

"Shutup!!!!"

Again, a restrained request for the mute button to be used was made.

If you think about it, entire careers can be derailed because of not pressing the mute button. Even worse than not remembering to press the mute button is accidentally unmuting yourself with your cheek while squeezing it against the keypad. 

Fatal.