With a well designed pocket flipper, it is very easy with a little practice.Well, in my neck of the woods, for now, my gun is carried concealed. MANY people here carry a folding blade in the pocket top, or waistband. The problem with those is you have to (in your scenario) fish it out, then get it open with one hand, all while fighting for your life (and gun) with one free hand. Low probability of success, compared to fighting for your gun, and trying to get to an eye, or a throat punch when you get a chance.
Emphasis on "well designed" which most are not.