Without reading the other posts, and at the risk of repeating something, the best bet is to either stay in your car and call 911, or calmly walk into the store, keeping an eye on the other guy.
I must say, however, that it is your responsibility to check traffic on both sides before changing lanes, and the incident in the parking lot didn't help.
I was in front of him at the light, we both turned left, and wanted to get into the right lane to turn right after the turn.
He decided I was too slow and tried to hurry things along. I did nothing wrong or improper.