This song is about a very large woman lead singer Bon Scott had relations with early in the band's career. In a 1976 interview with the band for Sounds magazine, their guitarist Malcolm Young prodded Scott to tell the story about "the fat one." Scott explained that backstage at a show in Australia, a rotund woman they called "Big Bertha" came forward when he asked, "Who wants it?" Too frightened to refuse, he did the deed with Bertha, who then called to her friend, "that's the 37th this month," and produced a black book where she recorded her conquests. Scott turned the incident into a song, this time naming the woman "Rosie."
In their early days, the band shared a house in Australia where lots of unsavory incidents occurred. This gave them material for songs like this one and "The Jack." Bon Scott had great affection for the full-size girls, and occasionally put his conquests in his songs. Another song on the album, "Go Down," mentions Ruby Lips, who is another real person. This is confirmed in the Let There Be Rock liner notes.
The music is based on the Chuck Berry song "No Money Down."
Bertrand - Paris, France
Originally released on the Let There Be Rock album, this song didn't get much publicity until AC/DC re-released it a year later on If You Want Blood, You Got It when the band became internationally popular.
This song was covered and performed live by Guns N' Roses. Nearly a decade later, Axl Rose cited an article in Melody Maker comparing the original AC/DC lineup to Guns N' Roses as the inspiration for covering this song.
Originally, there were two versions of this song. The first was called "Dirty Eyes" and was eventually released in 1997 on the Bonfire boxed set.