Continuity mistake: Melissa McCarthy wears an ace bandage on her left wrist throughout the movie. In the bridal shower scene the bandage is on her right wrist. (01:28:30)
Continuity mistake: When everyone except Helen start to show signs of food poisoning in the bridal shop, Becca puts her right hand over her mouth to keep from vomiting. The camera then switches to behind her but her right hand does not appear to be over her mouth anymore. It switches to in front of her again and this time, Becca has her left hand over her mouth.
Continuity mistake: When Annie and Helen are taking turns toasting Lillian, Annie goes up for a second time. In the close shot, she is holding the microphone in her left hand and a champagne flute in her right. The camera goes to audience, and when it is back to her, the flute and the mic have switched hands. In the next wide shot, the are back to their original position. (00:26:40)
Answer: The driver behind her couldn't see her brake lights and didn't realise she was stopping.
Brian Katcher
Plus the driver was also driving really close to her.
Turangaa_Maxx