It's happened to all of us. You're in the middle of something really important like a job interview, or your wedding, or an attempted abduction of a foreign dignitary when suddenly you hear it. Your phone. You forgot to turn it off and now it's ruining your life forever. FOREVER.
When this happens, it's important to stay calm. Don't overreact. That will simply draw more attention to what's happening. Just reach into your pocket or bag as calmly as possible and discreetly silence the phone. Kind of the way the guy in this video does.