The Best Supporting Actor category was established by the Academy of Motion Picture Arts and Sciences (AMPAS) in 1936.
Below please find my list of the weakest (least deserving) performances, honored with the Best Supporting Actor Oscar.
I have arranged them chronologically.
Walter Brennan, Come and Get It, 1936
Anthony Quinn, Viva Zapata, 1952
Red Buttons, Sayonara, 1957
Martin Balsam, A Thousand Clowns, 1965
Jason Robards, Julia, 1977
Don Ameche, Cocoon, 1985
Jack Palance, City Slickers, 1991
Cuba Gooding Jr., Jerry Maguire, 1996
Christoph Waltz, Django Unchained, 2012