Depending on the face of them man:
If he seemed to pull the gun out of fear, I would put my hands up and tell him I wouldn't say a thing. Once his guard is slightly down, I'd as quickly as possible, snag the gun out of his hand, kick him (yes, in the weak spot) in the crotch, put his arms in a twist behind his back and somehow with all my strength, get him on the ground. Then, if I knew how, completely pull apart the gun. Or throw it somewhere far from reach. I would scream on the top of my lungs to get all and anyone's attention. While he's on the floor, I'd try to keep him completely pinned down, and if possible, knock him unconscious with something that weighs A LOT.
If he seems to have the face of: I just want to kill -
I'd pee myself, scream, run and dodge anything I could, try to take him down while screaming and fighting with him. If I got shot, well shit. And I would keep on screaming. I have a very high pitched scream that'll make anyone cover their ears regardless to the situations around them. I'd use that to my advantage and try to gain control of the situation.