Kramer Impersonation (The Chicken Roaster, Season 8, Episode 8)
In this episode, a Kenny Rogers chicken place opens up across from Jerry’s building, and the light from the neon chicken on its rooftop goes right into Kramer’s apartment. This affects Kramer’s sleeping schedule, so he asks Jerry if he’d be willing to switch apartments.
They wind up switching apartments, and the outcome is great. Jerry comes barging into his own apartment as Kramer would, with his hair sticking up, and acting very much like Kramer. We can now assume that Kramer’s apartment is what makes Kramer, Kramer.