I had a problem with a squirrel years ago at the University of West Florida. People would get food from the vending machine and feed the squirrels, and this particular one knew to come over if people were there. Soon, if you didn't feed it, it would jump on you. One day, I went out to get a soda (thus, no treats for the squirrel) and over to me it hopped. I warned it by kicking my foot at it to stay away, but it jumped on me anyway. I grabbed it by the tail and slung it! It hit a tree and ran off. Later, the University trapped the squirrel because it was becoming a major problem and students were complaining about it. I don't know about them, but it never bothered me again.
I do think that feeding them may lead to this type of behavior (food aggression).