Weed leaves a stench on your body plus the whole glazed eyes bla blah, alcohol leaves a stench on your breathe, and benzos I mean its just obvious, "Hey, why did you just light like 3 cigarrettes in a row?" lol
MDxx is a perfect example especially in higher doses you'll be too fucked to notice you are drenched in sweat, clenching your jar like crazy, breathing heavy, talking to your self, ect; even if you do notice that false sense of security will prevent you from realizing that it is 100% obvious to anyone with half a brain what you are doing.