Hoaxes.

We've all seen them.  On Facebook, Twitter, other social media sites; those irritating messages that people keep passing on, thinking that whatever is being said is real.  One of the earliest ones that I came across on Facebook, was the "Becoming a Parent (Father/Mother) was the best thing to happen to me" which was supposedly a site for pedophiles.  I checked my "bible" (about such things), www.snopes.com, and they said it was a hoax.
Hoaxes take time to check. They can also be aggravating to find, when you have to find the right key words to bring up the right information.  However, my real thorny spot/annoyance, is when others do not take the time to verify (with Snopes or other sources) before reposting.  I actually go a step further.  After I have verified it on Snopes as a hoax (or other findings), I copy the link, and then I post it as a comment on their post.  Most people appreciate it, but not sure all do.
Seriously though, some of these things LOOK legit.  Years ago, the person who told me about snopes, did not check it first with a report that looked legit.  The "Penny Brown" story was circulating, and had a picture of "Penny Brown," and vivid details like it was real.  But I went ahead and verified first, then let this lady know that it was a hoax.  She was like, "I usually always check...but it looked so real."
I once told someone off for posting an urban legend without checking first.  I told him as nicely as I could, "I like getting the informational/personal stuff from you.  Like what is happening  in your life, making plans to get together, those sort of things...but please stop sending me the bullshit emails without checking their validity first."  Needless to say, I didn't hear from him for a while.
But seriously, my point is, don't pass anything before checking first.  Virus hoaxes run rampant, and even false missing kids notices.  Unless I know dang well someone has done a check, I won't repost without checking first, or at least asking the poster if they have verified the information before posting.  If people would look these up first, a lot of this misinformation could be eliminated.