I think by far the shadiest place I ever did drugs was in study hall in high school. There was one day that a girl in my neighborhood literally gave me about 10 30mg mixed amphetamine salt (generic Adderall) pills, and I ended up crushing up 2 of them and snorting them off my table with a rolled up dollar bill while the teacher was reading a book. A couple of kids watched me dude it, and a stoner kid sitting behind me cracked up at the sight. Cool thing was I managed to sell the rest of the pills for $3 bucks a pop, and back in those 15/16-year-old days, that was decent money. Oh, and I once took 5 1mg klonopins (without ever having taken benzos) before an in-school-suspension, passed out the whole day, kept waking up to a teacher yelling at me to quit sleeping, woke up in a chair in front of the principal's office, got up, walked back to study hall and slept the day away. I remember the teacher being pissed at me, haha, and with good reason.
I also used to constantly pop pills at the drinking fountain in my high school, and have snorted lines in parking lots at my community college, have popped pills in bathrooms at family functions, have smoked joints (and even bowls a few times) while walking down crowded streets or in alley ways late at night (a few times cop cars have rolled by during or right after the act and scared the fuck outta me. Smoked weed in my car too many times to count, did some lines of mephedrone in my girlfriend's sister's apartment (who thinks I'm a junkie and thinks I've corrupted her sister and that any of my drug use is terrible, despite the fact that she drinks daily and used to be a speed freak), and I accidentally left about half a line of powder and a cut straw laying on the floor of her apartment. Also smoking in dorm rooms and in highly visible balconies has also been common practice. So I guess all in all, those are my shadiest places. Not as crazy as some, but still I've had quite a few adventures.