Other mistake: In the opening of this episode the screen reads "3:50pm On a Wednesday." When Gino (Frank's Brother) is reading the letters meant for Shadynasty, he says "Meet me at the airport, Friday, at 5:00, Terminal C." The gang and Gina then go along to the airport that very afternoon - a Wednesday - to try and meet Shadynasty and get her and Frank back together. And of course she is there, despite it being a Wednesday, not a Friday.
Continuity mistake: Dennis walks up to the computer to see the guy claiming to be their father carrying nothing, he puts his empty left hand on the bar, but when the shot switches he is holding a coffee in that hand. In the shot right before the opening credits the coffee is gone again. (00:01:00)
Revealing mistake: During the training montage, right as Mac is about to smash the bottle over Charlie's head, you can see Charlie stop what he's doing about a half-second before being hit, and brace himself for the impact, despite not being able to see it coming. This is confirmed on the DVD commentary.
Continuity mistake: When Frank, Charlie, and Dennis are in the cop car at the red light, they're on a one-way street, with cars parked to their left (facing the same direction as the cop car). However, when it cuts to Frank, we see a car drive by in the opposite direction, and the parked cars are gone.
Visible crew/equipment: During the scene where Dennis and the Waitress, Mac and Dee successively walk into the back office to talk to Charlie near the beginning of the episode, in some of the shots, you can see outside the office door, and you can see the top of the set has no ceiling, and even see part of a stage-light.
Continuity mistake: While Mac is holding the picture of himself to Dennis & Dee, towards the end of the scene he is holding the picture with one finger around the middle on the top edge. Dennis then says "You're going to hell". The next shot he is holding the picture by its side with two fingers.
Audio problem: When the Vietnamese man is playing Russian Roulette in the end, a few seconds after picking up the gun, he moves his thumb and we hear the gun cock. However, you can see that he didn't actually cock the gun, as his thumb never came into contact with the hammer while moving, hence the sound was a phantom sound.
Continuity mistake: At the very end, while the gang is reading the new review and then talking about how their names weren't mentioned, a hammer appears on the bar between them, only to disappear a few shots from the end; Charlie then retrieves it from under the bar as they leave.
Plot hole: Early in the episode, it is mentioned that the serial killer is murdering "Young, attractive blondes", yet at the end of the episode, when the gang finds all the severed heads in the killer's refrigerator, almost none of them are blonde or young, contradicting what had been previously established.