Basically, if you smoke cigarettes or weed and drink alcohol, the game should give you low priority smells based on what you're consuming. These smells would last a short time, but can stack up and become more potent with repeated consumption, so it shows when you've smoked a full pack of black deth in an hour.
Of course, being low priority smells, any cologne or other potent source of odor would mask it, and smoking or drinking would not override such smells.
