@JimmyT said:
Perhaps Costa could send them a friendly note saying that he can see right into their kitchen and sometimes sees more than he would like … just so they know.
Costa, if you do send a note, make sure you put your name and contact details to it. That would minimise the risk that it is taken the wrong way. A young woman on her own getting an anonymous note about her appearance could be seriously creeped out by it.
More generally, I and various of my neighbours have, from experience, an abhorrence of anonymous notes.