Shoulder pain

About four days ago, I was goofing around with one of my coworkers. I went to push her away by moving my forward/ outwardly stretched left arm to the side. As I pushed her away and my arm crossed a 45-60 deg angle from the center of my torso, I felt a considerable amount of pain (enough to make me stop). The pain subsided within seconds. A day later, I went to close a padio door using the same motion (arm stretched somewhat outward, and then moving my left arm laterally outward). The pain reoccurred, but this time, I felt my arm come out of the socket slightly. I left go of the door, and my arm fell back in. I didn’t believe it happened, so I performed the same motion again, but with a lot less force. As I applied more force, the pain spiked and my arm "thumped" out of the shoulder socket, and then back in as I let go of the door. I used to always have pain in that shoulder when doing bench press (pinching sensation as the shoulder grew tired), until I started to spend more time strengthening the shoulder. I have full motion of the arm and shoulder with no pain or stiffness, and can bench press, although, benching weights in excess of 160 lbs causes a pinching sensation while performing the exercise. I don’t seem to have any swelling, although the shoulder did get "warm" after I tested it doing some bench pressing with increasing weights (to find the limit). Both arms, when rotating them in the shoulder sockets, would always create a "thumping" sensation in each shoulder socket, but never causes any pain. Any suggestions/ ideas?