There are some common misconceptions, received opinions, slips and so forth which really irritate me.
Here are a few of the most egregious:
"This begs the question..." No it doesn't. 99 times out of 100, when people use this phrase, they mean "this raises the question...". "Begging the question" is a term with a specific meaning, describing a logical fallacy where you smuggle in your conclusion as an assumption, thus appearing outwardly to prove something which you haven't in fact proved at all. This is such a useful term that it would be a shame if we were to allow the likes of Evan Davies (a persistent offender) to wreck it for us.
"If Napoleon had won Waterloo... .... he would have reigned peacefully as Emperor for decades". No he bloody wouldn't have. He would have had to face Blucher's Prussians within 24 hours, and then go on to face an even larger Austrian/Russian army under Schwarzenberg - who had kicked Napoleon's sorry ass at Leipzig - and even had he defeated that, he would still have been blockaded by the Royal Navy and facing open hostility from the whole of Europe. It bugs the hell out of me when people seem to assume that the Napoleonic wars were scheduled to end in 1815 no matter what, with Waterloo being a kind of "penalty shoot-out" with the winner taking all.
"Beautifully designed..." OK, so if this phrase is used on, say, Top Gear or The Gadget Show, I'm not quibbling. It's the careless use of the word 'designed' in writing or TV programmes about natural history that bugs me, partly because it is simply wrong and partly because it offers a shred of comfort to moronic creationists. Nobody designed it, it evolved.
I'm sure others have their own list of pet peeves, of some of which I am doubtless guilty myself; but having got that off my chest I feel curiously cleansed...