Songfacts®:

• This bawdy song finds Paul McCartney parodying someone he once worked with who was a bit of a pain. "To tell you the truth, she was someone we rubbed up against," he told Uncut magazine. "You get a few of them in life, these people who screw you over. I thought, 'I'll have you. I'll write a song. You never know it's about you, because I won't tell anyone. But I'll know. And people who know who I'm talking about will know.' So I drew up my dislike of this individual and make her into a song character."
• McCartney recorded this simple blues-rock song for McCartney III, an album where the ex-Beatle played all the instruments. He told Uncut the vocal was the first take. "If you will think you're doing a posh, important album, you might go over the vocal and think you can improve it," he said. "But this was: it will do."
• McCartney used for the song a vintage 1954 Fender Telecaster guitar gifted to him by his wife Nancy. "My missus gave me this beautiful little 1954 Telecaster," he said, "which I haven't played too much until this album, so it gave me a great chance on the lead part of Lil."
• "Lavatory Lil" echoes the character songs from The Beatles' later years such as "The Continuing Story of Bungalow Bill," "Mean Mr. Mustard" and "Polythene Pam."
  
  "What you do is you take half an idea of someone," McCartney explained to to NME, "you just make a fiction about what they do and what they're like."
• Some media have speculated that the song is about McCartney's divorced second wife, Heather Mills. But during an interview with The Sun, Paul was at pains to point out this is NOT the case: "I wouldn't want to upset people like that," he said.