How to disable automatic wifi connection? When OSX already knows an wifi network it auto connects to it, but when it doesn't know the wifi network it will auto connect depending of the setting of the "ask to join" toggle setting in system preferences.

How do you force OSX to ask to join for every wifi network, whether it is known or not?  I don't want OSX to ever connect automatically.
The only way to stop from automatically joining a preferred, or known, wi-fi network, is to not store the password for that network and type it in each time without clicking the "save password" button.

As soon as you save the password the network will be added to the preferred list even if the remember networks button isn't selected, and it will connect to it automatically (or rather it will connect to the first one on the list that is finds in the order in which you have them listed).