You drank a lot of booze: Your party the night before may come back to haunt you. High blood alcohol level affects the motility and permeability of the intestinal wall. This causes diarrhoea, loose stools and a change in the smell of your poop. Alcohol also contains high amount of sulfate, which helps the colon bacteria to make sulfide gas. Sulfide gas enters the stool and gives it an offensive stench.