Continuity mistake: Blank and Debi are in a club. All of a sudden there is a martini glass (neither of them are drinking martinis) Just when you have enough time to notice the extra glass one of Debi's drunk friends comes clambering over with a martini in hand. But then there is only one on the table when the camera pulls back.
Continuity mistake: At the end of the movie during the big shootout, we see Martin and Grocer shoot the two cops as they come through the doors. When they stop shooting we can see that Grocer is out of ammo (the sliders on his guns are back) and Martin is out of ammo only on the gun in his left hand (our right) as the slider on the right hand gun is still forward. Yet when he turns to face Grocer, both guns are empty and the sliders are back.
Continuity mistake: During the reunion when Martin and his friend are carrying the hitman down the stairs, the stairs are wide with a railing up the middle. The first shot of them, from the top of the stairs going down, shows them both going to the right of the railing. In the very next shot, from the bottom of the stairs showing them coming down, they are on opposite sides of the railing.
Continuity mistake: This mistake takes place at the beginning of the film, after Martin has shot the hitman on the bicycle. When Dan Aykroyd appears and kills the men in front of what appears to be a hotel (the intended victims of the man on the bike), he unleashes a barrage of gunfire from 2 revolvers. It's difficult to count the exact number of gunshots, but it is at least twice as much as the capacity of two revolvers (even if each weapon holds 8 rounds, which most don't). A typical Hollywood mistake, where reloading isn't needed.
Continuity mistake: When Martin is in Miami, he has to rush down the stairs and kick in the door (after his attempt at poisoning goes wrong). After he kicks the door open and fires one shot, (knocking the guy back on to the bed), as he proceeds to close the door and walk towards the bed it is clear that the slide is locked back on his suppressed Glock, either from a feeding malfunction or an empty magazine. After the angle to the man lying on the bed and then back to Martin, the slide on his weapon is once again in the forward position, and without any indication that he had either reloaded (unlikely since he had only fired one shot and a Glock 17 with a high capacity magazine will hold 17 rounds, plus one in the chamber) or corrected the "jam" and released the slide (it could have been done in the short amount of time given, but would have been audible).
Continuity mistake: One contributor grew up in Grosse Pointe and couldn't help noticing that their shopping district looks nothing like the one in the movie, there is no Grosse Pointe High school (at least not since around 1970) and there is no GP radio station. In fact, the only scenes that are actually Grosse Pointe are during the opening credits.