Love and Other Drugs

In 1996, Jamie Randall (Jake Gyllenhaal) is fired from a Pittsburgh electronics store for having sex with his manager's girlfriend. His wealthy brother Josh (Josh Gad) announces at the dinner table at their parents' (George Segal and Jill Clayburgh) house that he has found Jamie a job as a pharmaceutical sales representative. After attending a Pfizer training program where he has sex with the instructor (Kate Jennings Grant), Jamie goes to work for the company and tries to get doctors to prescribe Zoloft and Zithromax. He is rebuffed, much to the dismay of his regional manager, Bruce (Oliver Platt), who sees Jamie as his ticket to the "big leagues" of Chicago. Bruce says if Jamie can get Dr. Knight (Hank Azaria) to prescribe Zoloft instead of Prozac, other doctors will follow his lead. Jamie tries to get access to Dr. Knight by hitting on his female employees until, exasperated, Dr. Knight unethically permits him to observe him at work, during which time he accidentally sees a disrobing patient, Maggie Murdock (Anne Hathaway), who suffers from early onset Parkinson's disease.
Jamie angles a date with Maggie, who has sex with him. Jamie is later beaten up by top-selling Prozac rep Trey Hannigan (Gabriel Macht), one of Maggie's ex-lovers, who warns him to stay away from her and the doctors. That night, Jamie is unable to get an erection. Maggie teasingly says he should use the new erectile dysfunction drug that his company has developed. Bruce confirms that such a drug, to be called Viagra, is about to be marketed. Jamie soon starts selling Viagra, an instant success. Jamie wants a committed relationship, but Maggie refuses. Jamie confronts her while she helps senior citizens onto a bus bound for Canada to get cheap prescription drugs, and they get into an argument.
Two days later, after he waits the night before at the bus stop in his car, he greets her back. Maggie is touched that he waited, and they resume their relationship. Jamie spends nights at Maggie's apartment. One night, he tells Maggie that he loves herâthe first time he has ever said that to anyoneâand has a panic attack. Maggie calms him by saying she "said 'I love you' to a cat once". Jamie catches his brother masturbating to a sex tape that he and Maggie had recorded. Jamie asks her to go to a Chicago medical conference with him. She ends up at a Parkinson's discussion group across the street, and is moved by the people and their stories. Jamie meets a man whose wife is in the final stages of the disease, and asks for advice about Maggie. The man tells him to run.
After the convention, Maggie tells him how much she loves him. Jamie starts researching Parkinson's, and takes Maggie to different specialists around the country to have tests done. Jamie becomes angry and upset when he arrives at an appointment, to find out it has been rescheduled after they had flown in to see the doctor. Maggie sees that Jamie can only love her if there's a hope that one day there will be a cure, and decides to break up with him.
Some time later, Jamie goes to a restaurant and runs into Maggie, who is on a date. Bruce shows up and reveals Jamie has been promoted to the Chicago office. While packing to move to Chicago, Jamie finds the videotape recorder where he taped himself and Maggie talking about life. Jamie realizes he wants to be with Maggie, but her boss tells him she has left for Canada to obtain drugs. Jamie flags down her bus and tells her that she makes him a better person, and that he loves and needs her. She starts to cry and says she will need him more. Jamie decides not to take the job in Chicago, but instead he attends medical school and stays with Maggie.

Question: Who beats up Jamie?
Answer: Trey Hannigan.