Continuity mistake: In season 4, episode 5, Marty Funkhouser is speaking at his father's testimonial. During his speech, he says that his mother died 10 years ago. However this episode is based around Funkhouser's mother's sudden death despite the fact that Marty previously claimed that she died more than 10 years earlier.
Continuity mistake: This mistake really applies to two episodes in season 1. In The Bracelet, Larry is approached by a homeless man who thanks him for the Chicken L'Orange. As a result of this (and his unkempt appearance), the women at the jewelry store will not buzz him into the store. The mistake is that Larry doesn't give this man the Chicken L'Orange until the 7th episode, AAMCO. And it is not just that the episodes aired out of order. Because in the episodes between these two, there are references that show that this IS the correct order of this season. So this becomes a circular reference that can't possibly exist.
Continuity mistake: When Larry and Jeff are at the restaurant and the waiter's arm catches fire from lighting the flambé dessert, Larry puts it out by pouring water on his arm. The wide shot shows the flambé dessert is no longer on fire. But on the next wide shot, the dessert is on fire again.
Continuity mistake: Season 5, episode 1, "The Larry David Sandwich." After Larry's near-death experience, he's at a party talking to Jeff and drinking from a very small cup. At first Larry's fingers are in the handle, but when he actually starts complaining about how small the handle is his entire hand is cupped around the cup.
Plot hole: In the final episode of season 6, Larry tries to find the name and phone number of the woman he was talking to in the waiting room. The receptionist begins to list the names on the sign-in sheet until she reaches 'Paula'. Larry nods to this, however Paula never told him is name, nor was there ever an off-screen moment when she could have. She could have been any of the women the receptionist named.