From my view this is a reason why the charging infrastucture needs to have lockable chargers. You should be able to park your vehicle and charge as long as you need or wish. If the issue is not having enough of charging points then this should be addressed instead of generating some Code of Conduct between EV drivers.Then you are a dick !! I will unplug your charger and do not give a rat ass if you like it or not.
Certain incentives can be put in place to discourage the improper use. For example parking without plugging could equal to 50$ ticket. Plugging without intention to pay could equal to 100$ ticket (plugin without swiping membership/credit card just to fool the cops). Plugging after full charge could equal to 3x charge rate. And so forth. These penalties might need some tought tho