I don't really have an issue with Mayfield picking a fight with a few fans. Its juvenile, but harmless and does little in his ability to be a good QB. Guys use different things to motivate them. If Mayfield has to prove that fan wrong, then good for him.
I do think Mayfield needs to become more professional overall. Someone posted a picture of him at the beginning of the year and end of year with his press conferences. I don't think you need to wear a suit, but if you are the face of the franchise, you should look and act like it.
He is talented and played very well at times last year. Plenty to work with and if you can harness his attitude and passion, he could be a great player. They need to hire the right coach to do it. I have very little faith in the Browns to do that