These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Periphery Demographic: Particularly the Live Action series. It's on CBBC, the intended audience could stretch to high-schoolers but assume for the most part they're looking at the 9-12 demographic. The show beat out other adult comedy shows for an award, and the first two series have been re-edited into an adult version hosted by Stephen Fry. Arguably, the writing allows for more of a Multiple Demographic Appeal, but its popularity is largely this trope. Also counts for the books.
Squick: A lot of the facts in the books and series are just disgusting.
Even Rattus, the rat announcer who laughs at most grisly facts and openly admits to eating filth, is disgusted by the Mellified Man mock-advert, based on the real truth that in Medieval Arabia, a popular cure-all was flesh taken from corpses that had been pickled in honey for a hundred years.
Rattus: "Y.U.C.K Yuck. And that's not a word I use often."
Tear Jerker: In some books, especially the ones about the World Wars.
Terry Deary has a real gift for finding the humour in the worst possible situations in Horrible Histories, but in Frightful First World War, he manages to sum up the worst part of the war after telling the story of men making new friends during the Christmas Truce.
"Having to kill somebody you like, that's the horriblest history of all."
When the books stop with the jokes and start getting serious when talking about real life stories, chances are you're in for tears. Of special note are the stories in Measly Middle Ages (a girl unwittingly betrays her castle, kills her betrayer, then commits suicide) Frightful First World War (a German spy, on the night before he's executed, asks for his violin and plays through the night) and Savage Stoneage (an aging archaeologist commits suicide because his theories about ancient civilizations have been proved wrong and he believes he's wasted his whole life.)
Acceptable Targets: To a certain extent. They get away with a surprising lot of irreverence toward traditional sacred cows, but they're also a) a children's show and b) one focusing largely on Western European cultures. Thus any controversial aspects of Arabic, African and Asian cultures are entirely avoided.
Oliver Cromwell and, by extension, the Puritans, thanks to the whole "ban Christmas, makeup, sports and theater" thing that happened once Cromwell took power over England. It gets mentioned in two of the Stuart-era songs and one Stuart-era skit is Cromwell throwing his own relatives in prison for celebrating Christmas.
Actor Shipping - Oh boy howdy yes. Pretty much every member of the main cast with everyone else, with a healthy selection of the supporting cast thrown in for good measure. The most popular ship, however, is likely "Baybond" (Mathew Baynton and Ben Willbond). This wasn't helped by the hair sniffing between the two during the original Alexander the Great sketch.
Draco in Leather Pants: The "Dick Turpin" song is all about Dick Turpin not deserving the Draco in Leather Pants reactions he apparently gets. Of course, given their plan for this was to take the resident Mr. Fanservice, dress him up and put guyliner on him, then have him sing about it, one can wonder how well they actually thought this through.
Ear Worm: "Stay calmer when you want to harm a llama, call a llama farmer!"
Growing the Beard: As of the second series, or more specifically as of all the awards the second series won, and the adult adaptation that resulted there from.
Hilarious in Hindsight: On the TV Show, on one of the funniest World War One sketches, there was one scene where one of the military officers shouted 'Austria and Germany, sitting in a tree! K-I-S-S-I-N-G!'. Then if you have watched Axis Powers Hetalia... It becomes hilarious.
In the "Phillip and Mary" sketch, Phillip responds to the Priest saying "how about a kiss?" at his and Mary's wedding by kissing the Priest. On the cheek, but still.
Also, the Historical Paramedics:
Geoff: Nigel, treacle!
Nigel:(puts hand on his shoulder, tenderly)Yes, honey?note "Treacle" is a term of endearment in Britain.
Geoff: No, no, get the treacle.
In the Admiral Nelson sketch, as he is mortally wounded during the battle of Trafalgar and deliriously mumbling, Lieutenant Thomas Hardy happens to hear him say "Kiss me, Hardy." Hardy then starts to argue with the ship surgeon that yes, Nelson really did request 'a bit of a snog'.
Charles II and Thomas Blood ("The man who tried to steal the crown jewels"). Charles — while looking like a puppy — is saying "I love him". Or earlier: "You must come round to the palace for tea."
The camp Pharaoh who clings to the Viking's arm in the cosmetics ad sketch.
Read up on Spartan pederasty. Then watch the "Spartan High School Musical" number.
And then there's the extremely camp Georgian gents Lord Humbertold and Lord Cumberland in Series Four who somehow manage to ooze Ho Yay by doing little more than standing next to each other.
Jerkass Woobie: The show's version of George IV has overtones of this. It helps that Jim Howick has a singing voice fine enough to actually make fits of royal self-pity touching.
Painful Rhyme: Some of the song rhymes can be a little strained. In "Boudicca", for instance, she mispronounces "woman" so that it can rhyme with "Roman."
Portmanteau Couple Name: Spoofed in Victoria & Albert's love ballad: "The press watched every smile and flirt/Called us Alboria, but I preferred Vicbert!"
Tear Jerker: It's mentioned the Heartwarming page, but the sketch based around the Christmas truce turns right into this towards the end. After the soldiers have exchanged their greetings, we return to the modern day sports announcers. What really makes the scene a tear-jerker is the look on their faces, but what they say counts as well, especially with the quiet pause after it. After all, they know how it's going to turn out.
Steve: Touching scenes there. It's hard to know how these troops are going to go back to trying to kill each other tomorrow.
Other Announcer: Maybe they won't, Steve. Maybe they won't. *pause* Merry Christmas.
Steve: Merry Christmas.
Another good example comes in the first series, after a skit about children signing up for the Hitler Youth. It's a shining example of Mood Whiplash done well, as the usual background music drops, and there is not a single pun uttered as we are informed of how children in the Hitler Youth were effectively the only protection for the German capital by the end of the Second World War.
These actually pop up quite often. The treatment of the Aztecs under the Spaniards starts off funny, as a computer game called 'Warrior,' and devolves into Rattus explaining that the Aztecs had little chance against the superior Spanish weaponry - and none for the Spanish germs. Ten thousand died of smallpox.
What Do You Mean, It's for Kids?: Mostly averted; yes, it's theoretically aimed at eight-year-olds, but the Parental Bonus is so very obviously deliberate — up to and including Word of God insisting that it's a 'family show' — it doesn't become a major issue. By its final few series, adult critics were openly writing of it as simply "one of the best comedies on TV."