According to one of the guys, a former referee, you can say “whatever you want when the ball is on your side of the court.”
I questioned this with the example of a tournament singles match I had and my opponent was running towards my drop shot and said clearly (to me?), “I can’t get it.” So I stopped being ready, as he got to the ball and hit it into the open court for a winner.
My feeling is that something said with the intention of being distracting is (or should not be) allowed. The former referee says NO; they can say whatever they want.
How about your opponent is getting ready to hit a groundstoke and says something directly to you that includes your name?
Or, your opponent is returning serve and he says something that makes you think he is calling your serve out (but he is not); so you stop playing?
Or you’re having a long groundstroke rally and one of your shots comes right near the side line; and he shouts a word that you take for ‘out’ and he says “No, I said ‘line.’”?
He agrees that they cannot talk when the ball is ON YOUR SIDE OF THE COURT… and has an interesting interpretation of that rule: he says, the ball is considered “on your side of the court” the instant it leaves your opponent’s racquet.