Politics was for the most part absent from my dinner table this Thanksgiving, but George W. Bush's name did eventually come up in the discussion, and when it did, someone brought up that Dubya is a direct descendent (on his mother's side) of Franklin Pierce. After my joke about the Ostend Manifesto predictably flopped, I tried again with a line about how both presidency's were total trainwrecks.In light of the fact that Pierce was involved in a deadly train crash while on his way to his innaguration, that too was met with crickets. Apparently, 153 years later is still "too soon." So when does "horrible" become simply "historical?"Looking through US history, the Salem Witch Trials of 1692 seem like fair game. The Kennedy assassination is sensitive subject, but I can probably talk about James A. Garfield. It's okay to laugh about the Titanic, but what about the deadly Molasses flood of 1919?Generally speaking, the further you travel back in time, the safer it is, but even that has its exceptions. It was funny when Mongolian soldiers in Iraq made t-shirts that said "Back to Baghdad," but not so much when Serbians used the 1389 Battle of Kosovo to justifiy ethnic cleansing.