I think most are advocating avoiding the situation in the first place--I loved the comment about biker bars and ATMs at 2 am--common sense goes a long way. If you cannot avoid the situation, try to avoid getting so close to another that they can attack you. If you cannot avoid that, try to project the feeling that attacking you is a bad idea (for them). If they attack anyway, as soon as is tactically possible, get way from the situation. This can be an initial outrunning if possible, or after something that evens up the odds (grinding your heel into their instep, or the keys tricks you know already, heck, even an Aikido technique perhaps) but assume you will get cut in doing so.
I liked the bear analogy...not many folks want to try their Aikido on a bear or a lion, but a 240 pound drug crazed felon with a knife is probably not much easier to work with...