The word "Unfriended" was in use much earlier than suggested on QI, and can be found in Shakespeare's King Lear.
Jo Brand tells an anecdote about Arthur Conan Doyle, that he sent some friends a letter saying "All is discovered, flee immediately", and one of his friends then disappeared. This is something Mark Twain did, not Arthur Conan Doyle.
When explaining the jobs of "Nightsoilmen", Stephen Fry says "People had outdoor jacksies in those days". He probably meant to use the word "Johns" or "Khazis".
The photograph of the piece of knitting with "I woolly love you" in Morse Code knitted into it is shown upside down. This is particularly noticeable because the O in you (dash dash dash) and the I (dot dot), are in the wrong places.
While Alan Davies is discussing Cruithne, he has sweat stains on his shirt.