WTBH, here's a little something maybe you never knew about the law. ANYONE can sue ANYONE for ANYTHING. It is almost unheard of for the courts to bar the door to the litigant. I've seen it happen when some nut has filed the exact same thing 20 or so times, but usually there is some allegation that, if there were some merit to it, MIGHT mean they were entitled to relief.
Even people who have immunity from suit can be dragged into court. The case will be dismissed, but the suit can still be filed.
So yes, highly aggravating, and an abuse of the process, which is why you want to point that out every time he does it. Sooner or later the court gets onto the fact that he is getting his jollies by abusing you this way. The sooner you put it on the record and point it out, the less patience the court will have with him. If he starts getting fined for it, or locked up for contempt for it, then he might start to think twice about continuing with this sort of thing.