Turtledove

I once saw an AH about a world in which there had never been any Protestant reformations. The synopsis said that Rome had cut a deal with Luther by which he became Pope Martin I. Leaving aside the fact that everyone knows popes change their names upon election, he would have been, if anything, Martin VI. Or maybe Martin IV--When the second Pope named Martin was elected, he wound up being Martin IV because some secretary misread Marinus and turned Marinus I and II into Martin II and III. But he would certainly not have been Martin I. Turtle Fan 04:44, August 1, 2010 (UTC)

Nothing like a glaringly wrong detail to take you out of an AH. TR 14:35, August 1, 2010 (UTC)
Any historical fiction, really. I once read a WWII spy thriller by WEB Griffin. Actually I read two of them; they were supposed to be a continuation of a series he'd started many years earlier. The latter book sucked from stem to stern except for one entertaining scene where a bunch of spies were making up the identity of a fictional courier who'd never existed so they could plant misinformation about the Normandy invasion. The former was pretty good until it got to its very underwhelming ending, but all I remember about the story now, a hair over four years later, are two things: A bartender asking someone if he wanted vodka or gin in his martini, despite the fact that Americans didn't start making martinis with vodka until the 70s; and reference to Vice President Truman (This was 1943).
The sucky book had someone visiting the UK, reading a street sign that listed the distance to somewhere in kilometers, and trying to remember the conversion formula. Turtle Fan 16:10, August 1, 2010 (UTC)