Smartass rhymes with:
tass, alas, amass, ass, bass, basse, blass, bras, brass, cas, cass, chasse, class, crass, das, dass, depass, fahs, fass, gas, gass, glas, glass, gras, grass, grasse, harass, hass, impasse, jass, kass, klas, klass, kras, krass, lass, mass, mass., masse, middle-class, morass, nass, pass, plas, plass, plasse, ras, repass, sas, sass, sasse, surpass, tass, umass, vanasse, vass, yass
Smartass sounds like:
schmertz, smarties, smartish, smarts, snorts