Watts deliberately covers a star tattoo above her collar bone with makeup while getting ready to chauffeur Keith and Amanda, but when she's in the chauffeur outfit, the collar is high enough to hide the tattoo on its own.
Keith arrives home after taking his savings out of the bank and starts to go upstairs. He puts his sunglasses in his shirt pocket, but when his father calls him into the room, they're hanging from the front of his t-shirt.
When Keith's sister, Laura, is talking to her friends about her new "popular" status, she has a military-style vest on over a yellow blouse. When we see her jump down after being accused of being "false", the vest is gone, but immediately reappears in the next shot.
After Keith checks the oil in Hardy's car, he closes the hood, walks around the car, takes the gas out and puts it back, stands by the side of the car and picks up the money Hardy drops. During this entire sequence, you can clearly see that he does not have the dip stick in his hands but after Hardy drives off, the dip stick appears in his hands and is thrown away.
When Keith and Amanda leave Hardy's house at the end, Keith unfastens the top button of his shirt and he untucks it from his trousers. As he walks down the drive, and runs after Watts his shirt is tucked in again.
When Watts is shooting craps with the off-duty waiters behind the restaurant, as she counts out the money to place her next bet she's holding a cigarette in her left hand. In the next shot, her cigarette is in her right hand.
The goof item below may give away important plot points.
When Watts is walking away from Keith after the "practice" kiss, you can hear the sound of a drumstick hitting the concrete, indicating that she dropped one of her sticks. Despite this, the next time her hands are within camera range, she's holding two, without having picked the one up off the floor.