In the final fight in the diner, Whiskey's 6-shot revolver is fired at least 10 times without ever being reloaded.
While toasting fallen comrades, Merlin and Eggsy nearly finish the bottle of fine spirits. The level of liquid has fallen well below the label. In a longer shot, the level of liquid has risen up to the label.
During the opening car chase the traffic changes between going on the left-hand side, the right-hand side and all over the place at just about every turn.
On the plane the pool table is set with balls. After they go get the suits in the next room, the balls are no longer on the table even though the triangle rack is still on it.
At Statesman's Kentucky distillery, Champagne takes an unwrapped cigar out of a tube and smells it. A short time later, when he asks Tequila if he is feeling alright, he points at him with the cigar that now has a plastic wrapper on it.
While descending on the out-of-control ski lift, the high-speed spinning of the lift would have caused it to act as a gyroscope. Rather than swinging back and forth like it was it would have stayed in a fixed position.
When Harry gives a final salute to Merlin he uses a US Military (or UK Navy) style hand salute instead of the British (and Scottish) Army style hand salute.
The virus is consistently said to cause a "blue rash." A rash is, by definition, a skin condition. The ailment actually shown seems to follow veins, which are under the skin. However, the name "blue rash" first shows up on social media, implying it was coined by average citizens who wouldn't have known the difference.
The Statesmen's private airplane is clearly a version of a Boeing 737, which is a narrow-body aircraft. However, the interior scenes show an extremely wide cabin, even wider than most wide-body aircraft.
Poppy claims that she has distribution points for the antidote near every major city, but her screen also shows several distribution points in locations that are very far away from anything that could be considered a major city, such as in Kamchatka or Greenland.
Charlie's new metal arm is so strong he can throw a bowling ball through a concrete wall, but when he slams Eggsy into the ground with the same arm, Eggsy is unharmed. Charlie is not a robot and can obviously regulate the force with which he wields the arm, otherwise he wouldn't be able to do things like tie his shoelaces.
When fighting Bennie and Jet neither Kingsman thinks to use their hacking watches to deactivate the robots though they do use them, in the same battle, against other electronic systems. Poppy clearly has a knowledge of Kingsman technology, so she could have made them invulnerable to such infiltration. Furthermore, it's possible they could have tried this, unsuccessfully, off camera.
Harry's left eye was shot and he was given a pair of glasses with the left side darkened. But at Eggsy's wedding, Harry's glasses appear to have the right side darkened. This is because the scene shows Harry and Eggsy reflected in a mirror.
How did Harry Hart come back from the dead? He was killed in The Secret Service. It's literally explained in the movie, that he was revived by the Statesman agents using their serum. It is not a goof and is explained, in detail, in the film.
All Kingsmen, and even the King of Sweden, are shown sitting with their jackets buttoned throughout the movie. Jackets are to be unbuttoned when one sits down, and a royal figure or a spy posing as a tailor wouldn't make this mistake.
When Eggsy is asking for Tilde's permission, and the camera shot is taken over his shoulder, his phone shows his microphone is turned off.
In the end credit music listings, for Prince's song "Let's Go Crazy," the writing credit reads "Written Prince Rogers Nelson." It should say "Written BY Prince Rogers Nelson."
When the two Galahads confront Poppy in the diner, there is movement of crew and camera in the chrome window surrounds in the background, even when the characters aren't moving themselves.
At Statesman's Kentucky distillery, Champagne picks up a bottle of Tequila which quite clearly bears a UK excise duty label.
The tracking device that Eggsy plants on Clara is said to be absorbed by a mucous membrane. Eggsy is forced to resort to sexual contact for this. But there are mucous membranes in the mouth and stomach as well. Simply putting the tracker into something she would eat or drink would have done the trick.
If Merlin synthesized the formula and sped it up, then he knew its molecular make-up and could just as easily have created the antidote himself.
There is no way the president would have been able to have millions of human-sized cages built in just a few days. They could've been repurposed/requisitioned cages that were originally used for something else.
Given all of the technologies that Kingsman has, all failed recruits (such as Charlie) should have their memory cleared with the amnesia needle for their own security concern. It is questionable why a top secret agency like Kingsman doesn't have concern about this. However, this means Eggsy has to get amnesia too, which would defeat a major plot point.
When the antidote is distributed worldwide, it's given directly orally to several of the infected, who are instantly cured. But they also show the infected who were in cages walking out, cured - yet there was no way for them to have received the antidote directly orally.
All Kingsmen, and even the King of Sweden is shown sitting with their jackets buttoned throughout the movie. Jackets are to be unbuttoned when one sits down, and a royalty or a spy posing as a tailor wouldn't make this mistake.
When Eggsy is having dinner with Tilde and her parents, the King of Sweden explains to Eggsy that he should be addressed as "Your Majesty." Living in a monarchy, Eggsy should have known this already, particularly after his Kingsman training, which included a significant etiquette portion.
The King of Sweden is formal enough to lecture Eggsy about the difference between "Your Highness" and "Your Majesty", but he is willing to call him by his nickname, instead of using his real first name.
Poppy's narration refers to fifties nostalgia such as Happy Days (1974), Grease (1978), and American Graffiti (1973). While Grease was about the fifties, Happy Days and American Graffiti were about the early sixties. The tagline for American Graffiti was, "Where were you in '62?" It might be noted that when the latter two were in production the nostalgia was for a time only ten years earlier.
While speaking to Eggsy on the phone, Tilde mentions Björn Borg. She pronounces his surname with a "g" sound at the end, the way English speaking people would. As a Swede, she would pronounce it the Swedish way, which sounds more like "borry".