I had one of these moments in Sharyn McCrumb's Bimbos of the Death Sun
"Well...what does he want?"Bimbos is a murder mystery set at a science fiction and fantasy convention. People encouraged me to read it because I was a fan of science fiction, science fantasy and murder mysteries. What could be better? And part of the fun, I was told, was figuring out all the inside jokes. What best selling author was this character a send up of and which former best selling author was being made fun of in that scene.
"I don't know!" wailed Perry. "Something called 'Smarties' and 'Yorkies.' Drugs, I expect."
"No, Miles. It's British candy. Smarties are like M&Ms, and a Yorkie is a chocolate bar." Being a Canadian gave Diefenbaker an occasional cultural advantage over his more insular American colleagues.(19) 
One of the most common descriptions of the book was "well observed" and everyone assured me that McCrumb was making jokes and constructing caricatures from the inside looking out not the outside looking in.
And then I read page 19. And after that page I could never quite trust the author again. For you see, I am a Canadian. I grew up seeing Smarties at every grocery checkout counter. I grew up seeing Smarties at every convenience store. I grew up getting Smarties on Hallowe'en. If I was asked if Smarties were a drug I would never, ever think to say that they were a British candy. I might say that they are candy covered chocolates that are vastly superior to M&Ms. I would not call them British.
So, if I can't trust McCrumb to get a detail like that right--why should I trust her about things I know less about that which candies are available in the convenience stores of Canada.
The rest of the book may be witty and full of inside jokes but I will never know. It lost me on page 19.
 McCrumb, Sharyn (2002). Bimbos of the Death Sun Rosetta Books