Can I scratch the top of a short male's head?
That sounds a little mean. What would compel you to want to scratch a man's head?
I don't like his hairstyle.
Making gestures like scratching someone's head to point out his crude hairstyle is condescending to them. It's better to keep your opinions to yourself and let people be who they are.
So now, I can't even talk to people anymore?
I'm sorry, but I want you to know that your actions might come off as rude and disrespectful. The person might take it as being ugly, and that might trigger self-esteem issues. I know you have good taste when it comes to fashion and style, so there is no point wasting time being a fashion police when there are just too many people in the world with bad fashion sense.