I started taking lessons once a week (had about 14 lessons). I mostly rode this quarterhorse mare that has been mostly friendly.
I am trying to ride this bigger appaloosa gelding and he oftens seems hostile to me. If i dont have food and just try to pet him, he tries to bite. When I try to brush him he moves away and sometimes raises his hind leg as if ready to kick. I see his ears go back which i read is a sign of aggression so I ease away but whenever i get close he does the same thing. He will sometimes raise his head high as well to be bigger than me. When he's grazing and i try to get his head up he will go back to grazing and sometimes paw at the ground if i put pressure to lift his head.
Yesterday when i tried to but him back in the stable he would stop following me at a certain point.

Around the owner/trainer, he's very docile and friendly.
He's only friendly to me too when she's around or if i have food in my hand.
I asked her about it and she just said he's being playful but she never sees him when he's being bratty. When she's around he's just playful.

I read horses that are comfortable around people establish a pecking order and so he probably feels above me in that order and below the trainer. I dont have this issue with the mare i ride, she's always very happy and even gives me hugs.