Scary Movie

An 18-year-old girl named Drew Decker (Carmen Electra) receives a threatening phone call while home alone one night. Drew is chased outside by Ghostface, who stabs her in the breast, removing one of her silicone breast implants. She is hit by a vehicle driven by her father, who was distracted by oral sex by his wife, and is then subsequently murdered by Ghostface.
The next morning, Drew's classmate, also an 18-year-old girl, named Cindy Campbell (Anna Faris) meets up with her boyfriend Bobby (Jon Abrahams) and her friends, Brenda (Regina Hall), Ray (Shawn Wayans), Greg (Lochlyn Munro), Buffy (Shannon Elizabeth), and Brenda's stoner brother Shorty (Marlon Wayans) . Various news teams, including hack reporter Gail Hailstorm (Cheri Oteri), converge on the school in the wake of Drew's murder. Gail hooks up with Buffy's mentally disabled brother Special Officer Doofy (Dave Sheridan), hoping to milk the facts out of him.
While Cindy is in class, she receives a note reading: "I Know What You Did Last Halloween!". She then realizes that Drew was murdered exactly one year after she and her friends accidentally killed a man during a wild car ride. At a beauty pageant that evening, Greg is killed by Ghostface in plain view, with the audience mistaking Buffy's screams and pleas for help as being part of her act. When Buffy realizes she's won the pageant, she almost immediately forgets about Greg's death and celebrates her victory.
After Cindy goes home alone, she is attacked by Ghostface. Cindy locks herself in her room and contacts the police, and Ghostface disappears. Bobby arrives momentarily after hearing the incident, but a pair of black gloves and a telephone fall out of his pocket, leading Cindy to believe that he was the killer. Bobby is arrested and taken to the police station. Afterwards, Cindy heads to Buffy and Doofy's place, to spend the night with them. When there, she receives a call from Ghostface, mocking her.
The next morning, Bobby is released, being found innocent as he was in the police cell and didn't make any phone calls. Meanwhile, Buffy, high on the success of her victory at the pageant, ignores Cindy's warnings about the killer and is beheaded in the girls locker room by Ghostface with a cleaver, though her severed head still remains alive. Ghostface, visibly annoyed, dumps Buffy's head into a Lost and Found bin. That night, Ray and Brenda go to a showing of Shakespeare In Love, where Ray is stabbed in the ear through a bathroom stall. Ghostface then goes after Brenda. Unfortunately, angry movie patrons, fed up with Brenda's rude behavior during the movie, kill her before Ghostface can.
Meanwhile, Cindy throws a house party, hoping for safety in numbers. During the party, Bobby and Cindy go upstairs and have sex, no longer making Cindy a virgin. Suddenly, Ghostface appears and apparently stabs Bobby, before disappearing quickly. Cindy gets a gun from a drawer near the entrance, Bobby follows and she tends to his wounds. Shorty comes up from the basement and informs them that all of the partygoers have fled the house. Bobby takes the gun and shoots Shorty, revealing that his wound was an elaborate ruse. Ray arrives on the scene, alive.
Bobby and Ray confront Cindy in the kitchen and announce their plan that they are going to kill her and her father (Rick Ducommun) despite the fact that they are not actually the killers. They also plan to make themselves look like heroes by giving each other stab wounds to indicate they fought back. However, the plan backfires when Ray stabs Bobby repeatedly, furious because his favorite show, The Wayans Bros., has been cancelled. Ghostface abruptly arrives and stabs Ray. He and Cindy then fight each other, but Cindy successfully subdues him by employing moves copied from The Matrix and kicks him through a window. However, Ghostface vanishes before the police arrive.
At the police station, Cindy and the sheriff (Kurt Fuller) realize that Doofy, the only person who knew about the car accident, was actually faking his disability and is the true killer. Unfortunately, Doofy has already escaped with Gail Hailstorm. Upon finding his discarded disguise in the street, Cindy begins screaming, but is soon hit by a car.
In a post-credits scene, Shorty appears and breaks the fourth wall by giving tips on how to survive this sort of "situation". They appear to be on how to survive in a horror movie, but turn out to be tips on how to successfully enact a "snatch 'n' run". In another post-credits scene, as part of a running gag involving Doofy and his Vacuum cleaner. He dons the disguise once more, to break up with his Vacuum. However after a bit of coercion, he has sex with it one last time.

Question: Who goes upstairs to have sex?
Answer: Bobby and Cindy.