My 4 yr old QH gelding has become fussy in his stall lately. When I approach his stall or occasionally when I am in the stall with him he pins his ears. He does not do anything else and it does not happen when I am saddling or brushing him. He was previously very friendly and would all but try to climb in my pocket for attention. Previously he always pinned his ears at feeding time but now it seems to be more often.
Nothing else has changed (diet, TO, etc.). There are no signs of pain or uncomforableness. He is still turned out the same (in only for bad weather or at least every other day for a few hours). His neighbor is one of his turnout buddies.
To me, that's sort of signifying that he's attempting to see if he can muscle you out of his way and establish himself as leader of the dynamic between you two. If you've ever watched two horses turned out together, if the more dominant one wants to move the other out of the way, the ears are always involved with the body language.
Make him move his feet. It doesn't have to be mean or nasty, just make him back up, drive his eye in a circle away from you, move his hind quarters away, etc. When it comes to feeding time, never just drop and run. You should be able to calmly place his hay/grain/whatever else where ever you want in his stall without him grabbing mouthfuls or getting in your face about it.
If your horse was an older gelding I would be worried (eg, look for health issues like ulcers), but at 4 yo, he's still finding himself. You're asking more of him under saddle and he's growing up, even though he's a gelding, he is changing physiologically. One other thing to look into is if his neighbors have changed. We had a horse that seemed to totally change behavior within a week, and it seemed to be because we moved a new horse next to him who didn't like him and was keeping him up all night - he became sleep deprived!