Like many cars, my car makes an annoying beep when you start the car with your seatbelt unbuckled; plugging in the seatbelt immediately ends the noise. I used to find this annoying, but I eventually realized it's a great ploy of Operant Conditioning; with classical negative reinforcement a user is quickly trained to avoid the annoying sounds by plugging in their seatbelt.
This has the devious effect of harming the UX of the situation (stupid sound!) but training the user to do what is safe, or more generally is a desired behavior of the user.
What other examples of simple Operant Conditioning are there in popular interfaces, physical or digital? I'd like to exclude deliberate Gamification systems such as achievements/ect as they're fairly obvious and more of their own specialized category.
Modal dialogs and pop ups also have the unfortunate effect of training users to ignore them but I'm talking about deliberate shaping of user behavior especially where the user is goaded into desired behaviors which presumably were desired to give a better user experience.