Put the phone down next to Monty Pythons theme tune playing in a loop on your iBone/Droid and walk off.
Or download and play this.
https://www.youtube.com/watch?v=P8hLKVoSgOo I have most of my friends in my directory. If the ring tone does not show a name I no longer answer it. On your mobile you can also set a block on numbers that pester you so they cannot dial you again in the future.
