L7 recorded the album as a trio formed by founding members Donita Sparks and Suzi Gardner, and longtime drummer Demetra Plakas, following the departure of bassist Gail Greenwood.

Unlike previous L7 albums, Slap-Happy features more varied and slower-paced songs, some of which borrowing elements from other genres like hip hop.

Upon release, the album received generally mixed reviews from music critics and suffered dismal sales partly due to the poor distribution and support by Bong Load.

[8] Although the album features several songs with aggressive guitar riffs that are reminiscent of the band's previous releases, as seen in the tracks "On My Rockin' Machine", "Long Green" and "Mantra Down", it also contains slow-paced and guitar-driven ballads like "Livin' Large" and "Freezer Burn".

"[4] The track "Freeway", which was referred by the band as "the feel bad dance hit of the year", features a hip hop-influenced style with sampled voices.

[12] To promote the album, a plane flew over the crowd during the Lilith Fair concert tour at the Rose Bowl stadium in Pasadena, California, on July 17, 1999, with a banner that read: "Bored?

"[1] The band supported the album with a U.S. tour that started on August 15 in San Diego, California, and ended on September 24 in Cleveland Heights, Ohio.

[14][15] In 2008, Sparks revealed that the album suffered dismal sales partly due to the poor distribution and support by Bong Load.

Marc Weingarten of Rolling Stone praised the band for "doing punk metal right", commenting that Slap-Happy "is all hopped-up, pared-down riffage with no apologies or gratuitous change-ups.

[8] Entertainment Weekly editor Natasha Stovall highlighted the album's different approach, stating that although the "neo-Go-Go's vibe" of songs like "Livin' Large" and "Little One" can be disappointing "for those addicted to the ultra-macha-punk throb of L7 watersheds", Slap-Happy's "harmonious pop sweetness" has "a super-catchy, Joan Jett-meets-the-Breeders feel that zestfully floors the accelerator.

"[22] Jason Hardy of Daily Nebraskan stated similar pros, noting that the album's new style introduced a "groovy" side of L7 that "most probably didn't know existed.

"[9] AllMusic's Stephen Thomas Erlewine described the album as "a respectable but predictable effort", stating that it "leaves very little lasting impression" even though "a few of the songs hit hard, and the band sounds energetic and muscular.

Erik Himmelsbach of Spin criticized Slap-Happy for essentially being the same as all of the band's previous albums, commenting "What was once fast and loose and dump now sounds lazy and stupid".