Yap! Yap! Yap!
From an Ask Mefi discussion on noisy co-workers:
Why avoid the argument? Bring one of those New Orleans noise makers to work, the sort you spin by holding a rod (noise thing buzzes loudly when you twirl it) While twirling it, scream "yap! yap! yap!" in their direction, for the duration of their talking until they shut up.
They might think you're a jerk, but do this every time they speak up! Soon silence will be yours.
Sweet, sweet silence.
I especially like the "yap! yap! yap!" Nice touch. Just another day at Misanthropics, Inc.