Worst smell I personally experienced? I think that was while I helped out at geriatric care and we came upon a patient that had little to no control left over bodily functions and thus had to wear diapers. He wasn't doing well those days and suffered from diarrhea in addition to the usual symptoms. Usually the smell of human excrements doesn't bother me overly much, but in this case it was an unbearably sweet, yet foul pungent odor.
I kinda suspect the medication had a hand in altering the smell.
From what I heard, but haven't experienced yet, I believe some fermented fish stuff is worse, though.