Add them to your favorites, bookmark, etc. It takes less than 30 seconds to determine if something is untrue. I will check them out, even when I know they are falsehoods and then "reply all" with a a link and a note encouraging folks to always check them out. Good folks are hurt by this stuff. THERE IS NO SUCH THING AS A LIE THAT DOESN'T HURT SOMEONE.. Or put another way, why would you WANT to pass on an untruth as truth? What is to be gained?
I have lost "friends" over my policy of not allowing urban legends/myths/lies to stand. Damn shame, really. But I believe that this is symptomatic of a much larger ill in society. It is just another part of the trend to only reading/believing those stories that support our biases. It is my opinion that the inability to challenge ones own biases is what allows slanted "news outlets" to flourish, to literally manipulate masses of people for their own ends, and is contributing mightily to the decay of society.
Bookmark those sites, folks, and lets take these types of things on.