So by you're definition a hunter is an irresponsible gun owner, a person who participates in competitive shooting is an irresponsible gun owner, A person who allows their friend to use their firearm while training them on safety is an irresponsible gun owner, a son using their father's shotgun while they squirrel hunt together is an irresponsible gun owner. I could go on with more examples of what almost anyone would consider responsible that by your definition would be irresponsible.
I'm going to give the benefit of the doubt here. I do not think you are claiming nay of the above are actually irresponsible gun owners. I'm assuming you're trying to say that an irresponsible gun owner is someone who uses a firearm for criminal activities or allows another to use their firearm for criminal activities. The issue here is most people would forego saying irresponsible and flat out say criminal.
My (and likely a high number of people's) definition of an irresponsible gun owner is:
#1. Someone who operates the firearm in an unsafe manner. This would include not always treating it like it was loaded, finger on trigger when not intending to fire, not paying attention to the direction of the muzzle/not always keeping the firearm pointed downrange.
#2. Someone who does not make a best effort to secure their firearms with children/underaged or someone who may be inclined to use a firearm in an illegal manner are living in the house.
We can agree to disagree on it, but saying a criminal is an irresponsible gun owner is playing semantics. A criminal is a criminal. Criminals don't care about responsibility or the law.