I don’t board, but years ago I took my greenie to xc schooling. It was packed. My horse was high as a kite from all the parking lot craziness, and I got on and aimed for the warmup ring. Whereupon there was someone lunging/doing in hand work. The ring was huge, but she was using the space right by the only 2 entrances, and while her horse wasn’t a complete hooligan, he was running around pretty fast. It almost blew my guy’s mind. I was able to get him to the back ring where they were setting up jumps, but they wouldn’t let me hack in there. I walked/jigged for about 20 minutes in that back ring, during which time the person had started doing close in hand work—having her horse back, pivot, etc., using a lunge whip. So I crashed her party and started warming up my horse in the big ring, and when my guy spooked stupid at something and upset her horse, apparently, she told me that she didn’t appreciate me upsetting her horse. ! We had a little ‘conversation,’ whereupon I advised her that unlike her I was sitting on my time-bomb and I didn’t appreciate her taking up the only warmup ring.
To me, that was common sense. But at the end of the day, I blamed the organizers for letting her lunge a horse in the only available riding ring on a busy xc schooling day. I mean, wtf? I know this isn’t the situation the OP is describing, but it made me aware of the issue and I agree with others—the barn should have clear rules about who can do what when and where.