How do you deal when someone tries to provoke you in the gym

Yesterday, when I entered the tight locker room in the gym a guy (as I saw him previously based on his body language, usually act like a dominant person) was standing in front of the mirror. He was already dressed, and I'm not sure what he was doing—possibly flexing his muscles—but he lowered his arm to let me pass through this small space. Then, he touched or brushed my hip with his hand, giving the impression that he was lifting it up again. I ignored it and moved on. I was pissed off later because, upon reassessing the incident, I think that he was intentially trying to assert his dominance. Given such a scenario, how would you respond/react?