It is possible that since his first exposure to Urban Cowboy, bar manager Paul John Kelley has been harboring a private fantasy shared by many men: to pour on a pair of vasectomy-inducing Wranglers and ride a mechanical bull worthy of Bud Davis. It's taken 18 years, but not only has Kelley procured an authentic "El Toro" mechanical bull from Gilley's -- the cavernous Pasadena, Texas, bar where John Travolta tried to gracefully two-step his way out of the 1970s -- he's also convinced the entire Slim's staff to join in his spur-jangled mania. During the three-day Rock 'n' Roll Rodeo, the 11th Street nightclub will be submerged in oil-town Americana -- red-white-and-blue banners, hay bales, picnic tables, and 20 tons of dirt suitable for chaw spittle. During the early evening, DJs will spin country music, old-fashioned rock 'n' roll, and western swing while folks cruise the parking lot for kicks, including beer carts, ring tosses, and a dunking booth containing some very dunkable characters, Slim's security guard Bob Johnson and M.I.R.V. madman Bryan Kehoe among them. Inside, folks can sit down to some Southwestern grub served by an appropriately outfitted staff or try their luck on the bull. The dirt mound oughta break your fall and make for some interesting dancing come nighttime when the live bands take to the stage -- Lane & the Badass Chicken Bones and Liar on Sunday; Crosstops and Liar on Monday; and Johnny Nitro and Big Meat Combo on Tuesday. No need to keep looking for love in all the wrong places, a modern-day Sissy awaits at 6 p.m. Sunday through Tuesday at Slim's, 333 11th St. (at Harrison), S.F. Admission is $10; call 522-0333.