Be angry at the situation, but do not confront the dog. When I was in grade school, they told us to look an attacking dog in the eye, to establish dominance and show him that you are not scared. There is a dangerous fallacy in this logic.
An attacking dog already believes he is dominant. In fact, he knows he is, which is why he feels confident in coming after you. No amount of staring him down is going to suddenly change his opinion about that. Direct, threatening eye contact is not telling the dog, "I'm not scared of you". It is saying, "I want to fight you." The dog will hand his letterman jacket to his lady friend, crack his knuckles, and be more than happy to oblige your request.
Stand sideways to the dog, with your shoulder facing him. This is a less confrontational posture, and it also allows you to look both at the dog and behind you, without turning your back. You'll need to glance behind you for potential escape routes, and also to avoid tripping as you retreat toward them.
Give Him Something to Bite - Other Than You
Hold something out in front of you, preferably something that will compress - a briefcase, purse, balled-up sweater or jacket, newspaper. The dog will be more satisfied with something he can sink his teeth into. But, any port in a storm. If all you have is your laptop or commuter mug, hey… Better it than you.
If you don't have anything on you, look around for a shield or weapon. Garbage can lids can be very effective. A broom or rake leaning against the side of someone's house can help to keep precious distance between his teeth and your supple flesh.
If you've gotten the dog to bite into your favorite leather jacket (you can buy a new one. You cannot buy new nerve endings), maintain a firm grip and engage him in a game of tug-of-war. Alternate between fighting back and letting him think he's winning. This will keep him interested, and not give him a reason to adjust his grip or go for a more auspicious point of attachment, like your leg or arm.