Continuity mistake: Towards the end of the film, we see Robbie enjoying the perks of a first class trip to Vegas. He is quite clearly sitting in the front section of a Boeing 747. However, the film cuts to several outside shots of the plane flying overhead. It is a twin engine jet like a 737 or airbus. The 747 has four jet engines and is much larger.
Factual error: Billy Idol didn't look that old in 1985 (sorry, couldn't resist it).
Factual error: In the scene when Robbie is going to baby sit his sister's kid, her husband mentions the episode of "Dallas" when they shoot J.R. That episode was aired March 21, 1980, but the film was supposed to be in 1985. It can't be a rerun, because he's surprised that JR just got shot - if it had happened 4 years earlier it wouldn't be a big story.
Continuity mistake: In the first wedding for the Veltrys, George finishes "Do you really want to hurt me" as Julia walks into the kitchen after having her bum pinched. Then the next scene is Robbie telling the drunk boy outside to go in, and in the background is George re-finishing "Do you really want to hurt me". Then George starts the song again as Robbie is not there. The intro is quite long to this song, but then the scene goes back to Robbie outside still helping the boy and the background noise is the middle of "Do you really want to hurt me." This is not possible.
Continuity mistake: When Robbie and Julia are talking together after the bar-mitzvah, you see Robbie rolling up the cord of a microphone, it cuts back to Julia, and she says something, then it cuts back to Robbie and it shows him finishing the cord. Then it cuts back to Julia again, and then back to Robbie, and he's rolling up more cord, but he couldn't have gotten another wire in that two seconds!