MD, good question. IF I care enough about that person, I will tell him/her, you're treading on my last nerve! If I don't care about the person, I'll ignore them. When in a situation where I have to interact with the dumbass who continues to be a stupid MF, I'll give them a hint. It takes a minute, but if I blow up that MF won't say **** else! They won't even talk to me!
The reason I take the time to explain to one and not the other is simple. People like family, my future spouse, my loved ones, and my <b>close</b> friends are folks that I want around me and LOVE unconditionally. Therefore, I give them a chance to straighten up. Otherwise, I save it so I can shut that **** down once and for all! You have to give them enough rope. Usually they'll hang themselves.