To keep myself entertained while at a bizarre meeting with a client, I sifted through a few popular history books our host had on his shelves. One of which was a generalised affair about decisive battles and blah-dy blah-dy blah. Went to the section about ancient Rome and dear god in heaven the author so obviously knew sweet fuck all about them. Errors in their constitution, biographies, historicity and even popular legends were ballsed up. I then had to tolerate the client's number two (probably in both senses of the expression) spout further crap... and I had to bite my tongue because they gave us a lot of business and it would've seemed very petty to my boss who was also present.
Worst bit was regarding the Second Punic War (discerning forum-goers will realise I know my shit when it comes that subject) and Hannibal & elephants, and the dictatorship of Fabius Maximus... who was one of eleven (twelve after a fashion) dictators who served during that was etc. etc. etc. It was just as well that it was a Friday afternoon and I felt too knackered to argue and wanted a whiskey more than an argument.
So, question: what's your area of expertise, and what pisses you off most that people get wrong most often about it?