to says something rocks ass is to say that it is glorious(good, great, grand...) in every aspect. The term can also be used when discussing the activites of homosexuals, but lets not get into detail. When using the term rocks ass never wear a backwards hat and/or a "varsity" jacket. If used correctly, "rocks ass" can be the life of any party!
Wow! This movie rocks ass!
Hoorah! Raffi rocks ass!
Wowzers! That man is an ass rocker!
HEEEEY! My new pants rock ass!
Woah! That lamp rocks ass! I absolutely have to have it!