They're one of the most prolific breeds in NYC, and either fall into the I'm-a-nasty-little-s**t category or I'm-the-sweetest-dog-ever category; there seems to be nothing in between.
Good socialisation and no mollycoddling is essential. They are fierce little dogs, and most dogs take those mini teeth very seriously. I kid you not when I say that this little guy--more than the Pits, the Rotties, the Mastiffs--rules the park on Saturday mornings.
(As a general guide, the long-haired chis generally have better dispositions.)