Punk Chick - S1-E22
Revealing mistake: While cuddling in the car Donna tells her boyfriend that she isn't wearing a bra when it is obvious that she is - at one stage when she leans toward him her sweater tightens across her back and the shoulder strap and clasp of her bra is outlined.
Revealing mistake: Before Jason Dean is shot outside the penthouse, Phoebe is waving her hands trying to convince him that the world is not real and you can already see blood on her fingers.
Revealing mistake: When Carrie bumps into Mr. Big and her purse falls, watch the people in the background carefully. Many of them are watching the couple talk and interact with each other. On a busy New York street nobody is going to pay attention to two people having a conversation. Apparently all these people were watching the shooting of the scene.
Revealing mistake: When Rachel and Adam first meet, their cars crash in the car park. In the shot where they both get out of their cars, you can see a dry patch of ground under Rachel's car, but the rest of the area is wet. Why would that space be dry, if Rachel just crashed and it isn't raining heavily at the time?