I think of the scene when MB called his son a handicap Sultan pointed a gun to her head and said do not call him that. Aryan is his weakness just like MB is R.K.'s weakness even though he will not admit to it readily. He had two of his "GOONS" on their motorcycle before his car, he could have easily sent them to do his dirty work but he wanted to vent his anger by himself. He did not sign the note hence R.K. is still guessing who the heck he is. And this is another way for MB to go see him. I think both R.K. and Sultan need to take a course on "Anger Management"... So to say it was cowardly or intelligent would be compartmentalizing Sultan because we do not know much about his character yet . But as you noticed R.K. in a second blamed MB for it. Angry men do not think before they do dumb things.