In the liner notes to the Rhino edition of the album, Costello writes:
"Less Than Zero" was a song I had written after seeing the despicable Oswald Mosley being interviewed on BBC television. The former leader of the British Union of Fascists seemed unrepentant about his poisonous actions of the 1930s. The song was more of a slandering fantasy than a reasoned argument.
The song therefore fits in with a number of others on early Costello albums that deal with themes of fascism and totalitarianism, which also include "Night Rally" from This Year's Model and "Goon Squad" from Armed Forces. In this case, a racist and totalitarian movement is seen in terms of sub rosa teenage sex: "Turn up the TV... Even your mother won't detect it/So your father won't know."
On his first visit to the United States, Costello substantially rewrote the lyrics to refer to Lee Harvey Oswald. This was a reference to the common misconception among American fans that this was the "Mr. Oswald" referred to in the original lyrics. This version is usually referred to as the "Dallas version" and is available as a bonus track on the My Aim is True reissue, and a live version can be found on Live at the El Mocambo.
The song was also involved in Costello's infamous performance on Saturday Night Live on 17 December 1977. Following pressure from his record company to play the song on the show, Costello began to play the song, but he stopped after only a few bars, saying that "there's no reason to do this song here." He then launched into an unannounced performance of "Radio Radio", a song he had promised not to play. As a result, he was banned from the show until 1989.