My mother in law is probably--no, definitely the worst about forwarding forwarded emails. During the election, it was much worse than it is now, but she's still pretty bad about it. And I swear to you, she believes everything she reads. I've argued the points about how those emails are almost NEVER signed. I've also argued the points about how they will often use words like today , tomorrow, next week or things like that and how given the way the email is forwarded (usually for years and years) who knows what that tomorrow originally was. The ones I find most offensive are probably the blessing ones. You know the type--you'll get good luck or blessings within the next 24 hours, but only if you forward this email on to 10 friends. And there's always that layer of guilt, too. If you don't pass it on, you must not care about your friends.
I really, truly, madly, deeply loathe forwarded emails. I am to the point now where I delete them all without reading.
I used to feel bad about the idea of telling my MIL about not sending them until I told her repeatedly about how viruses can be sent with those emails but she keeps on sending them! I figure that if she is allowed to not give a crap about possibly sending a virus to me, I can not care about offending her by asking her to not send the emails. Not that it's worked so far.