The following rules apply to the Kingdom of Camelot, ruled over by Uther Pendragon. The rules were not set down by him, however, and are to be taken extremely seriously. Also, SPOILERS ABOUND. Do not read unless you have seen all three seasons of BBC Merlin, and the newest episodes of season 4.
Rule Number One: Everyone Wants Merlin.
Seriously. He's like the pinnacle of desire in this show. Everywhere he goes, everyone he meets, no one can keep their hands off of him. Attractive new character in need of help? Usually they'll find a way into Merlin's bedroom. This is a very important rule, as it helps, intrinsically, to understand many of the following rules.
Rule Number Two: Shut Up, it's Fantasy.
Pertaining to both anachronistic anomalies and cultural anomalies: Where on earth did those tomatoes come from? Morgana's hair can't NATURALLY be that curling-ironed-perfect, can it? Since when do servants have salon-manicured nails? Should someone make a comment about how the only black characters are... blacksmiths? It doesn't matter. It's Camelot.
Rule Number Two Point Five: Close to Godliness
Anachronistic: Everyone in this show is extremely clean. Until Season 3.
Rule Number Two Point Five Point Five: Culturally Diverse
Cultural: In every tournament, there's some noble fighter who is not important to the plot, never focused on for longer than a few action shots, and is never mentioned in any capacity. Also, he's a ninja.
Rule number Three: "Eraah"
All the guards in Camelot are basically useless. The one time a guard got a line was the first episode, and it consisted solely of a badly aimed gesture and the sound, "Eraah." They are powerless to stop even the most mundane of threats, never mind live up to the high standard of keeping magic outlawed. Have you ever seen them do anything helpful or even somewhat guard-ly? Me, neither.
Rule Number Three Point Five: Bradley's Favourite
The dungeons below Camelot must be made of cardboard boxes, marshmallows, and toothpicks. Honestly. No one could stay locked in the dungeon for longer than a night if they were payed fifty gold pieces to do so.
Rule Number Four: The All-Mighty Slash Dragon
Everything the Dragon says to Merlin comes off as mystic wisdom, and Merlin is often left feeling confused at his riddle-like words. However, any idiot can see that Kilgarrah is simply trying to get Merlin and Arthur together. The fact that Merlin interprets the suggestions as ways to solve the episode's plot is completely coincidental and fortunate for him, but entirely unrelated to the Dragon's true intentions. Season one is comprised entirely of instances like this.
Rule Number Five: See No Evil
If you wear a cape, night or day, with a hood, no one can see you. No one. Especially not the guards.
Rule Number Five Point Five: Night-Sneaking
Once per episode, at night, Merlin (rarely quietly) leaves his room and (never stealthily) sneaks past Gaius to try and get to the bottom of whatever magical predicament he has found himself in the middle of. Merlin does not get paid enough to own a cape. It's a miracle and half that he isn't seen more often.
Rule Number Six: Sharpen My Sword and Clean My Armor... Oh, and Walk on Your Knees
Everything Arthur says to Merlin is intentionally suggestive. Everything Merlin says to Arthur is even more-so.
Rule Number Seven: KABLOOIE
Merlin is a murderer. Not just Arthur's protector and stuff- an insane MURDERER. Why does every person Merlin defeats have to EXPLODE? Search me.
Rule Number Eight: Dress of Evil-Doing
Morgana is a smirking wonder (it's incredible no one calls her out on all that devious smiling she does when something terrible happens), but what is more wonderful is her signature green dress. She has two, actually, but it basically boils down to the same thing- she's up to something, and it's probably going to be the plot of the episode. She also has what is lovingly referred-to as her "Cellophane Dress" which she wears to talk to (and lie to) Uther and Arthur.
Rule Number Nine: The First Code of Camelot
Well, it's never really the same THING, is it? One episode, it's "only those of noble blood can be a knight" and the next is "if you pick up a gauntlet, you HAVE to fight." It's always treated with the same level of seriousness, and is explained to Merlin in very somber tones. Must get confusing, what with it always changing to suit the needs of the situation- perhaps Uther sends out a weekly newsletter?
Rule Number Ten: Unfortunate Throwaway Female Character of the Week
This term has become the cannon description for every girl who enters the show for the sole purpose of hitting on Arthur and (sometimes unknowingly) putting him in harm's way. They range from white-blonde to golden-blonde to dark-blonde. The show does this so it is clear that Arthur does not belong with them.
Rule Number Ten Point Five: STAB HER.
You could say that the above has happened to Merlin, as well, however there was only ever one occurrence, and it ended in tears. Lots of tears. Except for the end, when Arthur basically tells Merlin that he's sorry for being such a prat, and they smile lovingly at each other.
Rule Number Eleven: Eyebrow of Doom
Gaius' face is incredibly expressive, and his eyebrows are the best part. One can judge the gravity of the situation based solely on how high Gaius' eyebrow has risen up his forehead. Bonus points if he's frowning with the other one.
Rule Number Twelve: Breakfast
Arthur loves throwing things at Merlin. He usually misses, which is funny because he can supposedly kill a chicken at a hundred paces. Perhaps he does it 'cause he loves him.
Rule Number Thirteen: Squeaky Leather Man
Cenred (of "Cenred's Kingdom") wins the prize for what is quite possibly the most impractical costume in the entire show. Leather panels over more leather panels, tied together with leather strings. The show is fond of close-ups of his various appendages, but only while he moves. Cue squeaking.
Rule Number Fourteen: What On Earth Is That Supposed To Be?
You'd think with all the money spent on cool spell effects and super-imposed location shots, the monsters wouldn't look so darn hideous. You'd think.
Rule Number Fifteen: Immortal
Sir Leon just won't die. Dragon kills every knight in the city? Oh, except for Leon. Immortal army killing everything in sight? Don't worry, Leon's fine. Every knight killed at the beginning of "The Coming of Arthur Part 1" is killed? Hey, don't sweat it- Leon gets resurrected. All without the aid of a sorcerer-manservant.
Rule Number Sixteen: Seduction Technique
In season 2, the audience grew accustomed to rarely seeing Arthur with his shirt on. By season 3, it was commonplace. Now, however, he's got quite an issue regarding his pants.
Rule Number Sixteen Point Five: BEWBS
Seriously. We understand the ladies of Merlin are well-endowed. We do not need to be smothered in said endowments progressively more each season.