Darling is shot in the right arm. Minutes later when she's eating in the diner, her right arm has no blood on it, and her jacket has no hole in it where she was just shot.
When the silver Ford Taurus is going into the crusher (after Baby is told to "sunset that ride"), just after the car is dropped into the crusher, the Taurus suddenly becomes a different car (the change is easily noticed by the different door handles), and in one shot, the engine appears to have been removed.
During the first heist Darling wears gloves going in and out of the bank but when she gets out of the car at the end of the chase she has no gloves on. So not only did Baby leave his prints all over the car Darling would have as well. Along with hair from everyone of them.
When leaving the post office, they shoot the security guard and in the rush leave their identity masking glasses on, however Buddy's glasses are turned off in one cut.
Debora is walking on the sidewalk in front of the coffee shop when Baby first sees her, but when Baby leaves, she's not there anymore. Based on her walking speed, she wouldn't have left that part of the sidewalk.
While waiting in the Subaru, Baby flips the wiper switch down to turn it off. In a Subaru and most Japanese imports, UP is off.
When Baby is shoving Buddy's car over the edge of the parking garage, Buddy fires his pistol until he runs out of ammunition. He then continues to pull the trigger with the result that his pistol dry fires multiple times. BUT when self loading pistols fire its last shot, the action will remain open (so that when a fresh clip is inserted the action will close and load the first round of the fresh clip into the chamber: making it ready to fire), and when the action is open, the hammer is held back by the action, which prevents the gun from being dry fired.
Before accelerating away from the post office dock, Baby presses a button to deactivate the passenger side airbag. There is no such button in the Mitsubishi Galant.
Baby is sentenced to "25 years in the Federal Penitentiary, subject to a parole hearing after 5 years served." BUT there is NO such thing as parole in the Federal Penitentiary system. There, one will serve their full sentence.
As lyrics are displayed in signs and graffiti in the opening sequence, the word "whoa" is misspelled as "woah".
In the opening heist, the getaway involves dumping the original car and switching to another. However, while Buddy, Darling and Griff all wear gloves, Baby does not. During his "dance" scene he touches, and leaves fingerprints on, the steering wheel, wiper control, the outside of the door, and a water bottle (which he leaves in the car). During the getaway he also would have left prints on the gearshift and the interior door handle. However, Baby has most likely never been printed therefore his prints would not be in any police records whereas all other heisters indicate they do have criminal records and could be implicated if their prints are found. This is also why Baby is asked to case the post office - he presumably has no criminal record.
During the course of the film, Baby frequently has music playing in his ears in order to drown out the tinnitus (ringing in ear) he suffers. However, most ear specialists recommend people with tinnitus to limit being around loud noises, which would include playing music via earbuds; Baby might being inflicting more damage to his hearing. However, he is also participating in armed robberies, which is not recommended as a healthy cure either. In one briefing scene, we see that Baby hears the instructions even though it seems he can't hear due to the music. This means he doesn't necessarily listen at loud volumes and only plays music enough to drown out the annoying tinnitus.
While planning for the armored car heist, Baby notes that Doc instructed them not to buy their Halloween masks at the same time (to prevent suspicion), yet when they get to the heist JD appears to have picked up all three of the (incorrect) Halloween masks. However, they could easily have ignored the advice as being overprotective or unnecessary.
During the post office robbery it is raining hard. When the getaway started, the sun was shining bright. However, the weather could have changed over time.
In the opening car chase sequence, several of the second unit stunt car shots show the driver as the only person in the car where there should be four occupants.
When Baby is high jacking the blue car he turns the ignition backwards to start the car not forward.
In the diner scene where Baby learns Debora's name, her Bo's Diner name tag says "Jonathan" on it.
When Bats, Buddy, Darling, and Baby go to the diner and order 4 Cokes, the sound of the ice clinking is ice in a glass cup but the cups are plastic.
When Baby is breaking into a car after being chased through the shopping mall, a camera operator can vaguely be seen in the reflection.
The camera crane is reflected in some shots of the second chase, especially when the gang vacate their vehicle in the middle of traffic.
(around 1 hr and 26 min.) When Baby heists an old lady's Chevrolet, the cameraman is briefly reflected on the car's windows.
(around 6 min.) When Baby and his gang switch from their red car into a green car, the cameraman and a crew member are reflected on the passenger's door upon swinging open.
(around 27 min.) As Baby and his gang drive off from their second heist, the camera is momentarily reflected on the Avalanche vehicle. Likewise, the camera crane is reflected on the blue truck - seconds later - as it tries to mow down the gang.
During the planning of the second heist, Doc mentions the bank is in Dunwoody, GA, at the top of the "Perimeter" (I-285), and that a possible getaway road is the Buford Highway. Later, Baby and the getaway crew are seen driving south on I-75/85 in downtown Atlanta. None of these highways or locations are anywhere near each other.
Oddly, none of the main characters seem to be too worried about leaving DNA samples at or near crime scenes or in getaway vehicles. This includes Doc, a purported criminal mastermind.
At the post office window, Baby plops down a $20.00 bill, asks for stamps, and is given back 3 bills in change (two $1 bills and 1 bill that the camera only sees the corner of), although he never told the postal worker how many stamps he wanted to buy, and she never asked. In 2016 forever stamps were .47 cents --increasing to .49 cents in 2017. In any event, there was no number of stamps that would yield 3 bills in exact change from a $20.00 bill.
Before entering the post office to scope it out with Doc's young nephew, Doc tells Baby to remove his earbuds and sunglasses. When the postal worker is signaled not to enter the post office on the day of the robbery, it is Baby in a car she wouldn't have recognized, wearing sunglasses and earbuds and without the young boy who hand previously accompanied him. It is implausible she would recognize a single customer she had only seen once before in his current circumstance.
At one point, Buddy refers to a "disabled parking spot". Almost all Americans would call it a handicap spot, while 'disabled' is used in the UK. The mistake is likely due to Edgar Wright, the screenwriter, being British.
When casing the post office, Doc's nephew Samm says there are "8 registers, 2 open" but Baby tells Doc "8 registers, 3 open".
Buddy cruises through the parking garage looking for Baby, calling out "wherefore art thou, Romeo?" Wherefore means why and not where.
Just before dropping Baby off, Doc turns right on a red light without stopping, and while the crosswalk signal is displaying a "walk" sign. Although one could argue that he is a criminal and is comfortable breaking the law, a criminal mastermind who plans heists knows how not to get caught and would never break two traffic laws in full view of the public (and risk being pulled over).