Songfacts®:

• At a beach-party-themed industry listening event held on June 14 2010, Perry explained that this mid-tempo party anthem, which recalls all the fun nights gone by, had a purpose for being on the album: "There's a lot of substance, but also some no-brainers," she said. Perry added that she likens the tune to "I Gotta Feeling" by the Black Eyes Peas.
• Perry was inspired to write this track after running naked through a park. She explained to Company magazine: "There's nothing better than an impromptu dance party with my friends. My track Last Friday Night (T.G.I.F.) is a song about debauchery because I had one of those nights in Santa Barbara. We went out to this place called Wildcat and got crazy."
  
  The Californian added that despite drawing from her own experiences in the tune, the raunchy threesome mentioned in the track didn't actually happen. She admitted: "We had a couple of beers and danced until we died, then brought the party back to the hotel room. Most of that song is actual truth, apart from the ménage à trois... unfortunately! But, yes, streaking in the park, that's what we did, so we had to write a song about it the next day!"
• The song's music video was filmed in May 2011. Perry created for the clip a nerdy 13-year-old alter-ego named Kathy Beth Terry, who is fond of astronomy and '90s teenage heartthrobs. Viral star Rebecca Black, whose hit single was titled "Friday" makes a cameo appearance in the video. Other well-known faces you may spot in the Marc Klasfeld directed clip include Glee stars Darren Criss and Kevin McHale whilst '80s songstress Debbie Gibson and actor Corey Feldmen play Kathy's parents. Hanson and saxophonist Kenny G provide the party's live entertainment.
  
  Debbie Gibson's character's first name in the video is Tiffany - kids, if you don't get why, ask your parents!
  
  The video was shot at Dukes of Hazzard actor John Schneider's house.
• An official remix featuring rapper Missy Elliott was released to US radio stations and digital retailers on August 8, 2011.
• When this single climbed to #1 on the Hot 100, Perry became the first woman, and second artist overall following Michael Jackson, to send five songs from an album to #1. The singer's previous four chart-toppers from her Teenage Dream set had been "California Gurls" (featuring Snoop Dogg), the title cut, "Firework" and, "E.T." (featuring Kanye West). Jackson notched his quintet of #1s from his 1987 Bad album.
• The song features a prominent saxophone part by Lenny Pickett, who has been the tenor saxophonist for the Saturday Night Live band since 1985.
• Darren Criss and Kevin McHale covered this song on the Pot o' Gold episode of Glee, having previously appeared in the music video. McHale told Billboard magazine it was strange for the pair to do things backwards to how they usually work: Says the Glee actor: "It's mostly Darren's song, I do some harmonies with him and he sings the lead. It's the first time it's been the reverse effect of we were in the video and then did the song after it. Adam Shankman directs that episode, and Darren felt kind of awkward about it I think. We talked about it, and then he talked with Shankman about it, the breaking the 4th wall aspect. It's backwards of how things normally work."
• This won Video of the Year at the People Choice awards, which were held on January 11, 2012. Perry won four other trophies at the ceremony, snagging awards for Favorite Female Artist, Tour Headliner, Song of the Year for "E.T.," and TV Guest Star for her cameo appearance on the CBS sitcom How I Met Your Mother.
• This song was co-penned by Perry's frequent collaborator Bonnie McKee. The pair had been close friends since they were teenagers and Perry decided she needed a co-writer that she could volley with for Teenage Dream. "I'd known Katy since I was 18," McKee told Billboard magazine. "After we got dropped from our labels, we used to play shows together- 'Last Friday Night' was actually inspired by Katy and my wild drinking days. We were in the same circles and always kept an eye on each other. We're still competitive: We always joke about being 'frenemies,' but honestly, Katy is such a great songwriter, she doesn't really need me. I owe all of this to her, in so many ways."
• This was the first song with a day of the week in its title to hit #1 on the Hot 100 since "Saturday Night" by Bay City Rollers topped the tally in 1976. It is also the only "Friday" song to hit #1.