At parties where I don't know anyone people hide their drug use from me, e.g. if I'm in the sitting room they go in the kitchen to smoke weed and if I walk in they don't offer it and look slightly embarrassed. Or if I walk past someone doing a dodgy dealing, or handling drug paraphernalia (e.g. heating up heroin), they shout things like "Walk on, Miss". A former neighbour was convinced that I had grassed him to his housing trust about his parties. So maybe I don't look like the stereotypical druggie.
P.S. On the other hand I have been followed around Waitrose probably because I was wearing a beanie hat and hoodie combo, and I was asked to leave an hospital waiting room (I had an appointment) because I was mistaken for a homeless person - it was in a posh town, I was carrying a very battered holdhall, I was very tired and slumped on the chair.