You've clearly not run games in public spaces.
I've had to point out what isn't acceptable more to adults than to teens at my tables. The store had to post rules on behavior... including, "Flush the toilet after use" and "Used paper towels go in the trash."
My own table rules are based upon years of both public and private, and are mostly about interpersonal at play issues, but when running a game in public, I still have to reiterate the "Wait your turn" and "Let them decide" aspects. And sometimes, "Please go wash your hands before we start." (Auto mechanic.)
When you make the expectations clear, people generally rise to them. A lot of times, gamers are poorly socialized. Not as strongly correlated as in the 80's, but still... making the list and letting people know ahead of time prevents a lot of stress later.