Disable AirPlay on a Mac
Unfortunately, Apple hasn't provided an easy way to disable this functionality. However you can deny global access to the application that provides AirPlay mirroring by changing its unix permissions

In order to disable AirPlay mirroring, we have to deny the computer access to the application that allows the computer to AirPlay mirror: Fire up a terminal and enter the following command:

sudo chmod 000 /System/Library/CoreServices/AirPlayUIAgent.app/Contents/MacOS/AirPlayUIAgent


Enter the administrative password and restart the Mac afterwards. If you try to AirPlay mirror to an AppleTV now, the AirPlay icon will stay blue, as if it's still trying to connect but it never will. 

The only disadvantage is that it locks up the menubar. The user won't be able to use any of the menu bar items after they tried mirroring the screen. You're still able to adjust the volume using the keyboard, though. Logging out and back in will restore the functionality of the menubar until you try to use AirPlay mirroring again.

To eliminate the temptation of using AirPlay you can hide the AirPlay icon by opening System Preferences > Displays and unchecking the "Show mirroring options in the menu bar when available" checkbox. You will need to repeat this step for every user on the system.