Thanks to a comment Paul made several years back about responded to his mom with Snopes links, I now commonly respond to forwards of false information was such, usually explaining what Snopes is and how one might consider checking their site before forwarding false emails, and cutting and pasting a few lines from the Snopes post disproving what ever the false claim is into my response.
I once had a coworker forward the
drinking cold water causes cancer/the right way to eat fruit to our entire office, which was full of new age ignoramuses who instantly started freaking out about the cold water thing, including one coworker who's husband has cancer. I checked Snopes, it was fake and responded as such. She sent out a friendly retraction email to all our coworkers, plus to her friend who had also forwarded it to his entire office as well as to her. His response to her, which she forwarded to me, was pretty bizarre. It was something along the lines of "why would you believe her over me? Do you think she's smarter than ME? Is she a doctor? This email was written by a doctor!" The version forwarded had a fake doctor's name at the end, which when googled only brought up hits related to the hoax. Odd that he took it so personally since it's not like he wrote the thing himself. Even worse was that he took the so-called doctor as an authority just because someone signed the email with a fake name with Dr. in front of it. I responded as such, and he responded with the wonderful "some people have too much time on their hands" response, to which I responded "It took me less than 5 minutes to check the authenticity of the forwarded email. Think of the amount of time and effort wasted for each person who believes they must eat fruit only at certain times and certain ways because of this message, and think of anyone who believe the information and no longer enjoys a nice cold drink of water out of fear." He finally surrendered after that, but I was still astounded that he held so firmly to believing the email that he felt the need to defend it.