Wouldn't it be so much easier if your cell phone rang super loudly right at that moment?
So here's the invention: A little ringer that you attach to your cell phone. Secretively, you put your hand in your pocket and activate the ringer. It's super loud. Loud enough to stop a blabbermouth dead in his tracks.
"I'm so sorry," you say, "but I have to take this call. It's from my mom."