Poppy revealed the title along with the tracklist to Am I a Girl? on Instagram.
"Girls in Bikinis" doubles as a critique on the sexualization and objectification of women in the media as well as an empowerment song celebrating revealing and skimpy clothing. The song uses bikinis as a focal point to represent these topics. The lyrics in the verses describe various articles of clothing that Poppy is wearing, as she dismisses those who believe that she needs to "cover up" or dress differently. In the bridge, Poppy invites men to wear bikinis as well, subverting the double standard that revealing clothing is acceptable for women and unacceptable for men.
The song may also implicate Poppy questioning her sexuality. Poppy mentions women throughout the song in a dreamy, fantasy-like manner. In March 2020, Poppy confirmed to a fan that [her] sexuality is "pending".
- 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", "Hard Feelings" and "The Rapture Ball".
- On October 5th, 2019, Poppy unlisted the YouTube audio for unknown reasons.
- In April 2020, the song would become a trend on Chinese video-sharing platform TikTok. Poppy also reposted popular videos using the sound on both her Instagram and official TikTok.
- A vinyl of the song with "Fashion After All" as its B-side was planned to be released for Record Store Day on November 26th, 2020. However, Poppy would later tweet that she did not consent to the release, and discouraged fans from buying it. Following this tweet, the listing was taken down from Record Store Day's official website.