bathroom etiquette

stop off at a lewis drug store to shop and mail a few things (there's a post office inside). lock myself in the bathroom for a while afterwards. drop a bomb. finish. stand up. buckle my pants. flush the toilet. (a lady's voice) "thank you for your business." that's odd. did i just hear that? did someone just thank me for my business? i flush again. "thank you for your business." one more time. "thank you for your business." scratch my head. walk out smiling - "your welcome!"