"Bottoms Up" is set in common time with a moderate tempo of 82 and is in the key of C minor. Mariel Concepcion of Billboard gave the song a positive review, praising Minaj's role, stating, Songz' part "fades in to the background" and that "Minaj steals the spotlight with a layered, almost cartoonish 16-bar verse that injects the track with much-needed liveliness and creativity", showing "more personality in 45 seconds than most rappers do in an entire song, balancing an aggressive attitude with her gentler side." The Washington Post 's Sean Fennessey described the song as "gleeful, kinetic" and viewed that Songz is outperformed by Minaj, writing " supplies a brilliant extended cameo on the song, and as she has on nearly all of her guest appearances this year, changes tempo, tone and persona in thrilling flashes". Or, maybe it's the infectious hook 'Bottoms Up, Bottoms Up.'" Andy Kellman of AllMusic called it "shamelessly mindless". Maybe it's the pounding kicks that keep my head nodding. BET Sound Off said, "two of the hottest things in the industry have teamed up for what might be a contender for the hottest joint of the 2010 Summer", commenting, "THIS ish right here is the perfect anthem for happy hour, the end of a hard day at work or even a stressful situation. It's getting hot in herre." WERQ-FM gave the song a positive review, commending Minaj's cameo. Ryan also gave the song a positive review, stating, "Trey Songz, sex inventor. Like his previous song, " Say Aah", according to Chris Ryan of MTV Buzzworthy, "is about the joys of enjoying a frosty beverage at the nightclub of your choosing." Ryan also said the song had an R. Minaj also sings breathily and references Anna Nicole Smith, and biblical figures Mary and Joseph. Minaj delivers her lines as in cartoonish voices and inimitable baby-talk, distorting her voice in parts to sound tipsy. Nicki Minaj appears in the song as herself, and her alter-egos, Roman Zolanski, and Harajuku Barbie. "Bottoms Up" features a "bass-thumping" beat. The person on DJ Khaled's ' All I Do Is Win' remix, that's Nicki, and the person on 'Bottoms Up,' that's Roman." Composition and critical reception Roman is crazy and Roman is weird and Roman doesn't care. I was gonna take that part out because I was like, 'Trey is gonna think I'm crazy.' Roman is very spastic. But then, all of a sudden, something just hit me. "I kept on hitting you like, 'I'mma have it done today.' I think I did live with it for, like, three days because I was changing it up, I couldn't get it.
When directing to Songz and also speaking to fans on her verse, the tribute to the late Anna Nicole Smith, and appearing as her alter-egos Roman Zolanski, and Harajuku Barbie, she said: She killed it.'" Minaj also stated that she had been asked several times when she would do a song with Trey Songz, and said when Songz contacted her she said she thought "This is our time". When I heard the verse, I was like, 'Oh my shit, I love her. Songz then addressed Minaj directly, stating, "I fell in love with you. Two, three days later I got a verse back that was just stupid." Can you come this weekend? Can you come down?' I stayed a couple extra days and she came through. I hit Nicki and I'm like, 'Man, I've got these two incredible records, I think one of them is gonna be my first single, and I need you to do it.
for BET Awards weekend, I'm working on a couple records, and I do this song called 'Red Lipstick,' and then I do 'Bottoms Up' the next day. In the webcast, Songz explained how the collaboration came together, stating: The song was intentionally leaked on July 13, 2010, and to celebrate the release of the song, Songz discussed the song with Minaj on Ustream.