Katrina
I don't have the links handy, but we went over Katrina exhaustively here (as you might imagine) back closer to the event.
I found out that a lot of facts don't match the mythology, including what was done by whom, rescue deployment timelines, engineering and contracting details, and a number of other issues.
Add to this the atrocious media coverage at the time, including some of the worst crap I've ever seen from Fox News, and political attacks and simultaneous ass-covering that would have most people thinking local authorities didn't even exist.
The memes are carved in rock now, and not much I can do about it, but
Popular Mechanics had a fairly good overall look at it a while back.