While there's nothing wrong with thinking outside of the box for a Halloween costume, there are some lines that should never be crossed under any circumstances. From costumes depicting victims of horrific terrorist attacks and mass shootings to references to famous child abuse causes—these costumes are seriously screwed up. However, if you're not sure if this year's costume is a no go, let this gallery be your guide for what never to do on Halloween. At least, not in the presence of trick-or-treaters. Take a look at 12 of the worst costume ideas in Halloween history below and let us know your thoughts on these NSFH (not safe for Halloween) costumes in the comments section on Facebook.