Sure, but you don't do that by slinging an insult. You (as you said) calmly and legitimately point it out. Just saying, for common example, "That was blazingly

Sure, but you don't do that by slinging an insult. You (as you said) calmly and legitimately point it out. Just saying, for common example, "That was blazingly stupid," isn't calmly and legitimately pointing it out. Calmly and legitimately pointing it out would be to connect the cause with the effect and highlight that the person didn't want the effect, like, "That's what happens when you touch a hot stove." The obviousness of the connection causes the person to see their own error rather sharply.