On a more practical level, ignore eye contact (unless you want a fight), but don't shy away - just get on with what you are doing. Interestingly with many animals, often strong males will make eye contact which may be a precursor to a fight. However, a child can make prolonged eye contact with a adult male and the male will just ignore it (because it isn't even considered a threat)..
Most predatory types are opportunists. In other words they are looking for the weak one in the heard. If someone has enough "juice" to scare you, don't look in his eye. O-Sensei warned the young deshi about this. He said something along the lines of do not look your opponent in the eye as he will steal your spirit.
On the other hand, what did O-Sensei do? He looked them in the eye and stole their spirit. This is why I have my students look at their partners eyes so they can learn to do this. One can always choose not to based on the situation.
Two things are usually present for the predatory type to decide to make his move. a) you don't look like you are paying attention, so he feels he can "ambush" you, and b) you look scared when he puts off his aggressive vibes. So, let him know that you are, in fact, aware of what might be comi9ng and aren't "open". This can be done by assuming a strong integrated posture, preferably not an aggressive stance and making sure the potential aggressor knows you are aware of him. Also, if you can pull it off while being calm and not fearful, do look him in the eye. Most of these guys are used to being aggressive and expect to see fear when they try to intimidate. When fear isn't present it tells them something isn't right about their plan.
However, it is very important to not be aggressive yourself when doing this. If you make it impossible for him to back off without losing face, in his own mid or with his buddies, he will almost certainly attack and now he knows you know something.
An alternative is the opposite. You pretend you are not aware of him, don't make eye contact, and let him think he has you and then decisively end it.
You have to know in advance what your options are so that you can make the best decisions "in the instant". There's no set approach and faking it won't work. Any good predator can see through that. If you don't have any technique behind you, as Lynn S pointed out, then you'd better jsut get away fast because you will not be able to stand there without being afraid and without being aggressive.