I stumbled onto a helpful Q & A from the CTC: 10 Common Questions about Cycling
Whenever somebody mentions safety I normally say “And people don’t die in car collisions or crossing the street?”. It always seems easier to make them feel less safe about their current travel arrangements than to defend the safety of cycling. I also sometimes ask them where they get the idea that cycling is unsafe from, are they quoting confirmed statistics or just because they can’t ride a bike safely? Generally I think this comes from their fear and I agree, I’ve never been on a horse, so in my head I’m going to snap my neck the first time I try and ride one, but it doesn’t mean horse riding is dangerous, err, is it?
The key to discussing cycling is to first know if the person is an idiot, don’t argue with them if they are, you know the saying 
Another approach is that you can always agree with them… “yes, bloody tree hugging cyclists, I know, but this driver this morning, I was stuck behind him for miles as he was doing 29MPH in a 30MPH limit during rush hour, can you believe it, some people shouldn’t be on the road should they?”
