When someone comes in for a hug, I take a step back and say "I'm sorry I'm not comfortable with touching." that's usually the end of it. Otherwise if the attempted contact is aggressive in nature I usually lower the tone of my voice and tell them not to *beeping* touch me.

Regardless of your reasons, you get to dictate your boundaries in our culture. If people fail to comply they are violating laws. I should make a I don't do touching button and start wearing it.