Character mistake: When Lucian tells Vlad that the creature he encountered is a vampire, Lucian says that "Pi" is Greek for "to drink". "Pi" is actually the Albanian word for drink, not Greek.
Character mistake: On the way approaching town the camera pans to a woman's hanged body with a sign written in German around her neck. One of the crew asked Wardaddy what it said, to which he answered something like "It reads 'I am a coward who refused to fight for the German people'." That sign actually translates to "I wanted my children not to go fight" or Anglicized for better effect, "I refused to let my children to go to war." Interestingly, once into town, there appears the corpse of a hanged man with a sign written in German that does translate to what Wardaddy said of the first sign. (00:43:00)
Character mistake: All the characters wearing gas masks are wearing them with the straps over the hoods. I was army trained, and you always wear the mask next to the skin for best seal, with the hood over the top.
Character mistake: When Chris joins the Marine unit they are going to breach a door. Chris removes his shooting hand from his weapon to signal the breacher. He would have used his support hand.
Character mistake: When Steve is at the Smithsonian, he reads the biography of his friend Bucky. At the start of the description, the bio reads "Born in 1916...", but at the bottom of the description, it reads "Bucky Barnes: 1917 - 1944." (00:18:35)
Character mistake: Baymax, a healthcare robot, says that his programming includes a database of 10,000 symptoms of disease. Yet, he issues the warning, "After eating, wait one hour before swimming." That warning, often given by parents to their children, has no basis in medical fact. People who do not get cramps after eating will not develop cramps by going swimming after eating: http://www.snopes.com/oldwives/hourwait.asp.
Character mistake: When giving Eggsy a tour, Galahad tells him that Oxfords are any formal shoe with open lacing. This is incorrect as Oxfords have closed lacing.
Character mistake: In the bathroom scene with the fat man tied up, Kevin answers his phone upside down.
Character mistake: When he called for a dinner reservation for 12 at his home it should have been 13, as he put 13 men down. (00:32:05)
Suggested correction: Actually 14.
It's possible he simply miscounted in the heat of the moment. I'm not saying you're wrong was John doesn't seem like the type to make this sort of mistake but it could be let off as a character mistake rather than a movie mistake.
A character mistake is a valid movie mistake and this entry is listed as such.
Character mistake: Dino puts up his "Elemento" for whoever takes down Marshall. Monarch then says there are only three of those cars (a Lamborghini Sesto Elemento) ever made. This is not true. Lamborghini didn't make three, they made twenty.
Character mistake: When the supply convoy is ambushed, Soto is instructed to get on the .50 caliber. However, the weapon on the gun ring is a .30 caliber M1919 machine gun, not a "Ma Deuce" .50 caliber.
Character mistake: Olson discovers a "microchip blocking the self-assessment program" and says, "it's a worm"! It is not. "Computer worm" is a type of malware that propagates over a computer network. What Olson discovers is an act of sabotage of malicious nature, but definitely not a worm. (00:25:39)
Character mistake: Nikki lost her insulin kit and needs insulin. Her mother suggests getting her a fruit juice, something sweet. Fruit juice contains a large amount of sugar which raises blood sugar levels very quickly. Therefore, people with diabetes are usually best to avoid drinking fruit juice. Her suggestion is absurd.
Character mistake: During the scene at the office of the University of Oxford, the Union Jack is hanged the opposite way from the proper position. (01:23:10)