So, knock on wood...I've thankfully never been in a bar or restaurant while it was being robbed!
However, I am 100% positive that if faced with that scenario, I would not react the way Tony Tovar did when it happened to him in St. Louis. Tovar was at one of the oldest bars in St. Louis, a regular watering hole of his, called Berhmann's, when a man with what local news channel KSDK called a "heavily modified pistol" entered and demanded money and phones from everyone. Tovar was so convinced that this man was not going to shoot anyone, that not only did he not give him his phone or money, but he kept drinking and even lit up a cigarette.
By the way, I strongly encourage against this. Check out the video!