Jimmy is the titular main antagonist of the Seinfeld episode of the same name. He is a man who always refers to himself in the third person.
Jimmy is first seen playing a game of basketball with Jerry, George and Kramer at the Health Club and wearing special training shoes which supposedly improve vertical leap. Later, At the health club Elaine tries to get the attention of the blonde man but ends up talking with Jimmy, mistaking his own declarations of interest in her for that of the blonde man because of Jimmy's peculiar way of talking about himself in the third person. Elaine thus agrees to a date with Jimmy. After Kramer visits Tim Whatley's office, He is drooling water all over the floor and speaking awkwardly because of novocaine. Then, because of the water, Jimmy slips while demonstrating some "new moves"—"Jimmy's down!"—and severely injures his leg—"Jimmy's got a compound fracture!"—and promises revenge—"Jimmy's gonna get you, Kramer! Jimmy holds grudges!" Elaine meets Jimmy again at the health club. She learns that Hank, the man she liked, is gay, begins to find Jimmy's manner of speech interesting, and decides to remain with him, declaring that she once tried to "convert" a gay man but will not try that again. At the benefit that Elaine and Kramer, Kramer is no longer under the effect of drugs. However, Jimmy arrives and punches him; Kramer's lip becomes swollen and he once again looks and speaks as if he is mentally challenged.