I open carry about 90% of the time in Washington State to include such places as downtown Seattle and SEATAC International airport. My experience is that about 90% of the public either never notices or shows no sign that they do notice.
Of the people that do notice about twice as many people have positive reactions as negative reactions. Most people who do notice the gun are either plainly supportive of it (thumbs up, saying something positive) or are genuinely inquisitive, ask about it, and go away having a better understanding of carrying firearms.
Of the very small minority of the public that I encounter who show some signs of disapproval, the vast majority and most vocal of those people have been the concealed carry only crowd that looks down their nose at me and says I should cover up my gun. Just because you would feel like an idiot and be embarrassed by your gun showing does not mean that feeling has any justification in reality evidenced by what those of us who open carry daily experience.
Examples:
Standing in line at Jack in the Box. Big guy literally looks down his nose at me and my gun and says, "I carry mine concealed." I replied, "You aren't very good at it." He asked, "What do you mean?" I said, "I know you have a gun!" No reply.
Leaving 7-11, I held the door open for my 13 year old daughter, a probably 6 year old girl and her dad. Our car was parked next to his jacked up pickup truck, so I waited on the curb while he lifted his daughter into the truck. I heard her say something like, "That nice officer is waiting for you." I was in a sweatshirt and jeans. When he passed by me, he said, "You should cover that gun with your sweatshirt." We were in a convertible, so my daughter heard him and she said, "He doesn't need to hide his gun, he's not a criminal!" No reply. I was so proud
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The reason I open carry is simple. Why would a common criminal, picking out the easiest targets they can find, pick the guy with the means visible to kill them to attack? Especially when 99.5% of the public does not appear to be armed? All they have to do is wait 5 minutes for the guy with the gun to leave or go down the street one block and have their pick of a plethora of targets that do not appear to be armed. I would rather the criminal just walk on by me and my family rather than put myself and my family through the trauma of defending against a criminal attack and the following legal battles. I have no desire to remove criminals from society. My hope is to deter the crime from happening to me in the first place, something that concealed carry can't do.
There has never been anyone able to produce an example of an open carrying Joe Citizen being shot first in a robbery attempt, and there have only been two or three cases presented over the span of decades of attempted gun grabs from Joe Citizens open carrying.