We got a bit more creative than that - you should invite them in to help you slaughter a lamb.

I personally go for the 'No, thank you' line - I find it very hard to be rude to strangers in person - I might flame them to pieces online, adopt my 'no one ever ignores me when I speak like this' tone on the phone, but in person I'm always polite - particularly when they have their children with them.