Poppy released the song as a surprise single. She did not make an announcement about the song's release beforehand.
"Hard Feelings" is about Poppy questioning her identity and being as a whole. She expresses confusion and questions whether she is a human or a robot.
Fans speculate that the song is a response song to Mars Argo and her fanbase. The lyric "What crimes will you make me commit?" could be a response to fans calling her an abuser in the wake of Mars' lawsuit against Poppy and Titanic Sinclair. Additional lyrics include Poppy asking the listener if she is a replica of someone they once loved, which could be an allusion to the lawsuit pointing out many similarities between Poppy and Mars Argo. Due to disagreeing with the accusations, she has "hard feelings".
- The French lyric "qu'est-ce que tu veux" translates to "what do you want?".
- The YouTube audio was originally titled "MD Poppy HardFeelings 1920x1080 full", as this was how it appeared as a YouTube notification.
- This is the second Poppy song to feature bilingual lyrics, with the intro incorporating both English and French. Her songs "Moshi Moshi" and "Voicemail" incorporate both English and Japanese, while "Aristocrat" also incorporates both English and French.
- Blame Candy guitarist Chris Greatti, who co-wrote the song with Poppy and various other songwriters, also performed the guitar solo in the song.
- In a 2018 interview with the Zach Sang Show, when asked about the lyric "Am I a man or machine?", Poppy explained that she would rather be a machine because they are smarter.
- This is the longest song on "Am I A Girl?", being 3:39 long.
- This was one of five songs on "Am I A Girl?" not to be played on the Am I A Girl? Tour, the others being "Iconic", "Aristocrat", "Girls In Bikinis" and "The Rapture Ball".