Just the last week or so he's started pinning his ears at anyone who comes towards his stall, but then puts his ears back up as soon as they get close.
I groom and tack him in his stall, and mostly he just lets me come and go, but occasionally he's started pinning his hears, squealing, and kicking his heels up a bit (only maybe an inch - just a threat, so far - I don't want it to escalate to more than that). I go in and out of his stall maybe 7 or 8 times changing brushes, getting his saddle, talking to other people - and he does this maybe once, or on rare occasion twice.
Mostly I've tried ignoring it, in which case it's over as quickly as it started, and he just puts his ears back up and acts like it never happened.
A couple times he got a little too close with his hind end and I pushed him away/made him move until his ears went back up. Then I let him relax.
During this same time, he's also started being the "big man on campus" out in the field. He used to be mostly a loner or just flit around among other horses, near the bottom of the herd structure. But lately he's kind of ruling the place. The barn manager has been making comments about it.
Under saddle he's an angel. Leading him around he's fine - knows to stay out of my space, listens to what I tell him. He stands well if I drop his rope, I can walk circles around him without him moving.
I'm just worried about this stall thing. I want to put a stop to it before it gets any worse. Any suggestions on the best approach?