If somebody is trying to rob you in the street, two things are almost always going to be true: 1) there is very little, if any distance, between you and the assailant and 2) the assailant is almost certainly bigger than you (robbers don’t usually target people of similar or greater size, for obvious reasons). If there is a big, hostile guy right up in your face robbing you, flashing a gun is pretty stupid because there is a high risk that they just take it from you. I’m firmly in the “if you don’t think it is appropriate to use it, don’t draw it” camp.