In the four years since Kathleen Hanna traded Bikini Kill’s rawk riot for Le Tigre’s synth-punk dance party, the international pop underground has gotten a lot more fun. Although Hanna doesn’t rap per se, her band’s drum-machine beats and speak-sung rants provided a road map for DIY punks looking to unleash their closet hip-hop freak. And when an androgynous Canadian temptress calling herself Peaches set raunchy rhymes to basement beats and trash-punk guitars on tracks like "Fuck the Pain Away," from 2000’s The Teaches of Peaches (Kitty-Yo), you could feel the script flipping beneath indie’s feet. Now we’ve got Oakland’s Gravy Train and Alabama’s Hawnay Troof to contend with: a pair of potty-mouthed, gender-bending rap crews with gay-sex appeal.

Gravy Train, who come to Axis this Saturday, are a quartet of three self-described "rap bitches" (Chunx, Funx, and Drunx) and one gay boy (Hunx) who apply riot grrrl’s postfeminist mandate to the Fat Beats and Bra Straps (Rhino) girlschool of ’80s hip-hop. Accompanied by little more than a chirping Farfisa organ and a beat-up drum machine, they sound sort of like Le Tigre if they were JJ Fad, or L’Trimm backed by ? and the Mysterians. Frontgal Chunx seems to have internalized Just-Ice’s 1986 anthem "That Girl Is a Slut" — and decided, like the grrrls who scrawled "whore" on their bellies in the mid-’90s, to turn the epithet on its rear. Their finest moment is "Drinking 40 Oz.," from their debut Menz EP (Cold Crush). In the spirit of Schoolly D’s "Saturday Night," Chunx recounts, in a squeaky bubblegum rhyme, the story of her day, and her love affair with St. Ides: getting trashed ("Don’t even try to contain the fortiez that I drain/I leave a malt liquor stain like a fuckin’ freight train"); picking up strays of both genders at the local high school ("I find me a bitch, a young virgin switch/I find a young gun, I drench him in cum"); eventually deciding she loves the booze more than the boyz ("rather sip you than get screwed").

GT’s debut album, Hello Doctor (Kill Rock Stars), adds a guitar and a sampler to the line-up, but the group’s gotten only more perverse. Like Turbonegro and John Waters, their twin turn-ons are fast food and grossout sex, a pair of infatuations that meet head-on in the surreal song "Burger Baby," in which Chunx gets impregnated by a hamburger. "I’m hungry, I’m randy, and I just can’t wait," raps Hunx on "Double Decker Supreme," a song about searching for the perfect three-way: "I’m fishin’ for sluts and using Chunx for bait!"

Puerile sleaze is nothing new in hip-hop, any more than it is in rock, but it’s taken18 years for someone to make the connection between 1986’s competing indie-label visions of debauchery: the garage-noise baiting of Pussy Galore’s Groovy Hate Fuck and the booty-shaking, strip-club funk of 2 Live Crew’s 2 Live Crew Is What We Are. Gravy Train’s union of those impulses, "Titties Bounce," is unlikely to get them admitted to Mensa, but until something better comes along, it’ll stand as the lone bridge between contemporary hip-hop’s commercial underbelly and Kill Rock Stars’ indie-punk rebel yell.

Among the guest stars on Hello Doctor is Hawnay Troof, a/k/a Chris Touchton — a member of Alabama’s teen-spazz synthcore brother act XBXRX, whose oeuvre encompasses the demilitarized zone between Killed By Death punk and laptop glitch-noise. On Hawnay Troof’s debut EP, Who Likes Ta? (Retard Disco), Touchton and his partner-in-crime, 900 Dix, reimagine Dirty South hip-hop through the foggy lenses of a pair of No Limit-type soldiers who happen to be flaming homos. The joke doesn’t get much deeper than is suggested by the song titles: "We Got Big Dix" (about "middle-class ghetto" kids holding up a bank at cockpoint), "All I Want Is Yo Dik," "13 Wayz Ta Get Hard," "Who Likes Ta Fuk? (We Like Ta Fuk)."

The EP’s no-fi production makes Manny Fresh’s early joints sound like Timbaland. But their rhymes are marginally on point, and the pair’s voicings — raspy barks somewhere between Mystikal and Flavor Flav — are no more (or less) offensive than Jon Spencer’s minstrel-blues yelps in Pussy Galore. Whether indie rock’s PC-reflex has become sufficiently desensitized to look the other way remains to be seen. (Initial reports seem to be in the affirmative: Touchton’s girlfriend, Bratmobile singer Allison Wolfe, has joined the group — which may also make it tougher to pull off the gay schtick.)

And Hawnay Troof is nothing if not a grand indie-rock in-joke: "Who Likes Ta Fuk?" samples a guitar squiggle from Bay Area no-wavers Erase Errata, and the disc’s one guiltless pleasure, a bona-fide bounce-rhythm dance tune called "Jump N Bump," grabs a lick from Kill Rock Stars gospel-punks the Gossip. The tortured ebonics of lines like "I call u ova with my dang a lang/but I can’t whait ta make u sang" (their spellings) are unlikely to win them any fans with the NAACP or Murder, Inc.; but given the balance columns, it’s gonna require a less cynical mofo than me to reprimand a gay posse — imagined or otherwise — for baiting hip-hop.