Ok, maybe that’s not what I would really do.
If I’m not in his line of sight, then like jimlongley said, move to cover and draw. Then I would use my weak hand to call 911.
If I’m in his line of sight, but the weapon is aimed at the clerk, then I would probably do nothing but become a sheep and a good witness unless I thought he was going to shoot the clerk. I know I don’t know for sure what he will do, but most robberies end without the clerk getting shot, and I could make the situation worse by drawing.
If he does shoot the clerk, then go to guns...
If the gun is aimed at me, get off the X, and go for my weapon or him depending on distance, his stance, available cover, his size/strength, etc. I’m not happy with having to draw against the drop, but I’m not happy with being shot while just standing there either.
Mike1951 mentioned the risk of multiple BG's...good point and if you can it would be a good idea to check your surrondings, including your six.
This all assumes I’m there without my wife…if she’s there my actions would be dictated by her safety.
And just for the record Todd, I for one like scenarios. Reading how others would respond, and the discussion of legal issues associated with those actions, is very informative for me.