Role in the film
Jimmy being Kenny's older brother, was likely abusive to Kenny, which caused him to be a bully himself. Eventuly, Owen, Kenny's main bullying target, stood up to him at a skateing rink, and struck him on the ear with a metal pole. While the bullies left Owen alone, they decided they wanted revenge, and Jimmy decided he wanted to join them.
One night, at the swimming class, Jimmy, Kenny and the others light a fire outside of the center to get coach Zoric's attention. Jimmy breaks into the pool area and scares off the students. In the confusion, Owen attempts to make a run for it, but is cornered by his lockers. Owen pulls a knife on them but Jimmy isn't inimadated. They drag Owen back into the pool area and throw him in. Jimmy takes Owen's knife, and decides to make an impossible bet; if Owen is able to hold his breath for three minutes, he will simply cut his cheek, if not, he will cut his eye out. Jimmy sarcasticly tells Owen to take deep breath's and holds him underwater. Eventuly, Jimmy is told to stop, to which he replies "shut up". At that point, Abby, a vampire Owen befriended, breaks in and starts to attack the bullys in a horrific, albeit offscreen, frenzy. Jimmy was the first to die as his head is ripped off.