On "Seinfeld," Kramer starts using butter in place of shaving cream. The gag appears in "The Butter Shave," the first episode of the show's ninth and final season, which aired in 1997. Kramer discovers that butter seems to make an effective shaving lubricant and enthusiastically treats it as an overlooked household innovation.
The joke expands beyond shaving. Kramer rubs butter over his body as part of an improvised tanning attempt, but the sun heats it and leaves him effectively frying himself. The episode uses his impulsive experimentation to create one of the series' most memorable pieces of physical comedy.
The title makes the answer easy to confuse with another product or with Kramer's broader butter-related scheme, but the specific replacement for shaving cream is simply butter. It is a comic premise, not a recommendation: butter is greasy, can clog a razor, and is not formulated for skin or shaving.
The episode also includes separate storylines involving George's apparent disability, Jerry's relationship with comedian Kenny Bania, and Elaine and Puddy enduring an awkward flight together. Its shaving plot remains the source of the episode's title.