Revealing mistake: When Irma screams at seeing Mr Bean with his jumper pulled over his head, all of the other cinema patrons jump with shock - except for the woman directly behind the two of them, on the right of the screen. She just grins and laughs, forgetting that her character shouldn't be in on the joke.
Continuity mistake: When Mr Bean is trying to get out of the car park through the entrance, he uses a wheelie-bin to simulate a car to get the gate to open. After he's out and shifted the bin, he's blocked in by another car. We see a hand take the next ticket (presumably belonging to the driver of the incoming car) but the car pulling up in front of Mr Bean is so far away from the ticket machine its not possible for him to take it and drive into the car park in the short amount of time seen, plus we never see or hear anybody get out of the car to get the ticket.
Continuity mistake: Just after Mr. Bean's hand is stomped on by one of the boys, and he lets go of the diving board, the camera pans back to show him falling into the water, but the same shot shows no-one else standing on either of the diving boards. The two boys should have still been standing on the higher one.