In the case

of the cursory glancer, it is advisable not to hold
eye contact. If you are sure that it is just a cursory glance
and not a challenging stare (it will usually be very obvious)
just
smile, perhaps say, 'hello' and then break the eye contact.
This will probably leave him thinking; 'Oh I must know him,
where do I know him from?' The ritual is then broken at the
very first stage. If he does ask you what you are looking at,
just apologise and say that you thought he looked familiar. If
he asks you if you want trouble say 'no'. This will usually
end the confrontation because he will feel as though he has
won and wander off to his cave. This will be hard if you are
a male with an ego to feed, but a lot easier if you are a
confident person that does not need to hurt people to prove
your masculinity. Women rarely have a problem with
submissiveness. Unless a woman has been brought up with a
weak male role model it is not normally in her nature to be
the 'protector'. If the latter is the case, she may have
developed male characteristics to balance the loss in her
environment, one of those characteristics being the ego. If
you are still approached put up a 'fence' (to be detailed) and
prepare for a physical encounter.