I'm going to tell a person to stop because he was holding his arm over my shoulder
I am not sure I understand. Is there any reason why you didn't want him to do that?
I don't like to be touched by people I am not related to.
It is wrong for people to touch strangers. You have the right to not be comfortable with it and should tell him next time you don't like it.
Why is everyone trying to make me feel like a piece of shit when I have a right to have my preferences?
You should be honest with this person. It is good to have boundaries in your relationships.