I cringe to imagine the tweet frenzy about to ensue daily in the Oval Office. Trump has no control. He can't even be loyal to his own vice presidential nominee or his party. I don't know what his agenda is - let's hope there is one - but I am not confident in his ability to master his impulses.
Yes, Donald Trump is too thin-skinned to be president. In order to be president, an individual must be able to ignore criticism and do what is best for the country. Donald Trump has shown himself to be too sensitive to do this, and will most likely prioritize tweet wars over governing.
Trump lets the smallest things get to him. He cannot handle a little bit of criticism. The first sign of someone talking bad about or opposing him, he jumps to Twitter and acts like a two year old. This is not the temperament needed for a person who is about to be in one of the most powerful positions in all the world.
It's true that Trump is a little bit thin-skinned, but it is also true that he knows how to say no. Trump doesn't want to pander to other countries. He tells it like it is. That means being able to be offended when another person or country does something that is out of line.