how to disable airdrop?

Airdrop will show in the Sidebar - unless you click on it and have another Mac nearby with it enabled there, there is no way another Mac can access it. It will only send files that you initiate in particular and also have to "accept" before it can be sent to yours. So, no worries as long as you do not have it highlighted (activated).

An other way to totally desable it is to go to settings, restrictions, and to turn airdrop off.. that way it won't appear anywhere...

You can prevent clicking on it by removing it from the sidebar, by command-dragging it off the sidebar, or by unchecking this option in the Sidebar section of the Finder preferences (located in the Finder menu).

https://discussions.apple.com/thread/3197984?start=0&tstart=0

Duh - didn't even think of that - thanks for adding!!

Are these instructions for a computer or an iDevice (since we are discussing Mac OS/computers here)?

Oh sorry yes It is for an iDevice, didn't pay attention to that...

just drop the airdrop to trash in order to turn it off.

Trashing OS components is not a good idea.