nudge phone to shut up

i'm sitting in a quiet meeting. suddenly calengoo starts shouting the details of an upcoming appointment. or it starts ringing, or whatever. it's buried deep in my pocket, but still sounds like the speaker is dangling in the middle of the meeting, and it takes a long time to excavate, unlock, and volume down.

what i want is to just whack it, while it's still in my pocket, and have that be enough to tell it to shut up. it's got an accelerometer, right? is there an app that can do this? tasker maybe? if so please clue me. if not, maybe it'll be my time to learn to make one.