Milton Berle
Milton Berle hosted SNL on April 14th, 1979 and his participation caused a lot of stress. Rosie Shuster, one of the show’s writers, said that watching rehearsals with him was like “watching a comedy train accident in slow motion on a loop.” His hijacking of the rehearsals caused him to be banned from hosting again, and his episode was not rerun since then.
Frank Zappa
Frank Zappa hosted the show in 1978 and apparently did a “disastrous job of hosting the show,” was accused of mugging the camera, and even let the audience know that he was reading off of cue cards. Following this horrible job of hosting, he was banned from the show.