I agree that Mc is made up bullshit
Boy do I have bad news for you about every other word that exists in every single language. There is no word tree we harvest fresh ripe new words from, everything is made up. We are just meat squirting air through our various holes because we like the sounds they make and wish to communicate thought.
Is it really so hard to respect a person enough to address them with the courtesy title they ask you to use? Are you in any way inconvenienced by saying "Hello Mx. TWeaK, how are you today"?