RSX- gas smells wierd...

Hey guys...every once in a while when i drive my car it smells like bad gas (when i get out or open the window)...it smells like something bad...bad gas- "dirty gas"...any one know what it is...is it maybe i put a bad gas in it...it doesnt smell that terrible but it SMELLS...i think i may have put bad gas in it...sometimes i get out of the car or open the window and i can smell it smelling kinda bad...i know it's not from the engine..but from the back (maybe where the exhaust is---maybe...)..any1 know???

do a search on "rotten smell" i believe. it's common.