John Riggi is Bank Teller in The Invitations (Season 7 Episode 22).

John Rubano is Man in The Postponement (Season 7 Episode 2).

Johnny Silver is Ice Cream Vendor in The Understudy (Season 6 Episode 4).

Jon Favreau is Eric, the clown in The Fire (Season 5 Episode 20).

Jon Gries is Homeless Man and Rusty in The Beard Jerry (Season 6 Episode 15) and The Bookstore (Season 9 Episode 17).

Jon Lovitz is Gary Fogel, George's and Jerry's friend in The Scofflaw (Season 6 Episode 13).

Jon Manfrelotti is Guy in Police Lineup in The Beard (Season 6 Episode 16).

Jon Polito is Silvio in The Reverse Peephole (Season 9 Episode 12).

Jon Voight is Jon Voight in The Mom and Pop Store (Season 6 Episode 8).

Joseph Maher is Gavin Pollone in The Dog (Season 3 Episode 4).

Joseph Malone is Michael, Robin Sandusky's husband in The Good Samaritan (Season 3 - Episode 19).

Joseph R. Sicari is Willie in The Secretary (Season 6 Episode 9).

Joseph Ragno is Marty in The Wife (Season 5 Episode 17).

Juan García is Jaime in The English Patient (Season 8 - Episode 17).

Judge Reinhold is Aaron, the close talker in The Raincoats (Season 5 Episodes 18-19).

Julio Oscar Mechoso is Julio in The Kiss Hello (Season 6 Episode 17).

Kay E. Kuter is the head Latvian Orthodox priest in The Conversion (Season 5 Episode 11).

Keith Hernandez is Himself in The Boyfriend (Season 3 Episode 17).

Keith Morrison is the Newscaster in The Trip (Season 4 - Episodes 1 and 2).

Keith Sellon-Wright is Guy in The Muffin Tops (Season 8 Episode 21).

Kelly Perine is Usher in The Postponement (Season 7 Episode 2).

Ken Hudson Campbell is Ken in The Seven (Season 4 Episode 14).

Ken Kerman is a police officer in The Beard (Season 6 - Episode 16).

Ken Takemoto is the Chairman in The Opposite (Season 5 Episode 22).

Ken Thorley is Vic the car salesman in The Mom and Pop Store (Season 6 - Episode 8).

Kenneth Ryan is Mr. Burns in The Maestro (Season 7 Episode 3).

Kevin Dunn is Joel Horneck, a childhood friend of Jerry's in Male Unbonding (Season 1 Episode 4).