Remote log in/conference when they leave their desk. Hide the tab saying “you are in a conference call”.
When they come back, edit all their emails as they are typing.
We had one guy flip out and stand up screaming that some tucker was going to get a smack if they didn’t stop.
Then IT changed some settings, you get an unhideable banner across the top of your screen these days. Bastards.
Looking at someone and smiling then going back to what you were doing works well if you can get half a dozen or so doing it. Unless it’s someone likely to flip. 😳