Years ago I was walking through a park area of UC Berkeley while on vacation and this squirrel walked right in front of me and stood there, so I stopped and watched it. I realized I had some food in my backpack and there might be something squirrel-appropriate, so I very slowly took it off and opened it up, hoping the squirrel wouldn't get scared and run away. I found something - like a grape or something, don't remember what - and got it out to toss to the squirrel, but when he saw it he ran up my pants leg and stopped at about my waist. Scared the crap out of me. I held out the food and he took it with one hand, stuck it in his mouth, and ran away.
That's when I learned that there are apparently tame squirrels all around Berkeley.