SalaamualikumwerahmetAllaahewabarkatuh,
I completely understand where you sisters are coming from. And you know what, shying away, or staying quiet is not necessarily the answer. You sisters have a right to protect yourselves from mens' lustful glances and the that get into everyone's heads.
From personal experience I can tell you that for the men that just continue to stare at you, or even approach you, and perhaps start talking or saying something perverse, then BE TOUGH. There are alot of perverted people out there, some of whom are Muslim men. And they act like they are the predators and us sisters are the prey. Should you be scared and show that you are uneasy? NO. Look at them straight in the eye and show them attitude. Look them 'up and down' as if you are disgusted and stay away. If you have to speak up to get them to back off then SPEAK UP in a direct, and strict manner that shows them you are NOT one to be made a fool of, or one that can be easily approached.
I understand that we should keep our gaze down as well, but it really depends on which type of men you're talking about. Perverted men you must show them that you're not this vulnerable girl that they can play around with or harass, and if that means getting straight in their face and telling them to stop looking or that you're not interested then "Just Do It"-This is your dignity and protection we're talking about.
With Muslim men who maybe just keep glancing back at you, perhaps really for marital proposals, then what I find best is to show absolutely no concern-get off of your seat on the bus and go somewhere else, stick a book in your face, etc and InshAllaah they get the point. If they try to approach you, then be strict in your voice and tell them you are not interested. Otherwise, just remind them, 'please dont stare; remember Allaah'.
And of course, as a reminder to us sisters, including myself, we shouldnt be giving them anything to stare at in the first place. This is crucial because so many times we feel hurt and abused by men looking and approaching us, that we focus on them only being the problem and not realizing that perhaps we are contributing to their actions. What I mean by this, is a woman can be wearing a scarf around her head, but her body curves still show-clothes that are too tight, etc. Or she could be wearing Abayah and scarf yet she has eyeliner, shadow and lip gloss, perfume on. Or even just showing that you have an 'approachable' personality, by smiling all the time, laughing etc can make it easier for a man to approach you, rather than the hijabi beside you, who seems a little more serious (i.e in front of men and not in front of her friends)
I know I wrote a lot but I just get so enraged when men stare and at the point where I am now, I understand how important it is for a woman to defend herself (esp when she doesnt have someone who can do that for her, like a mehram), esp around perverted men.
For the brothers out there, Allaah forgives the first glance but that doesnt mean you specifically and intentionally look at each woman that passes by at least just one time, thinking 'its halal'. If youre looking for marriage, then InshAllaah do it in the most halal possible method. If you have a sister in mind then its all the more reason to stay away from her and guard your gazes and thoughts since you have her in mind for marriage. Also, if automatically you pick up the clue that the sister is uncomfortable, then perhaps you should take this as a sign to mean she is not interested in the first place and just stay away.
*No offence meant to anyone, InshAllaah forgive me if I sound rude; im just extremely passionate about this issue because sisters are always scared and dont know how to defend themselves and there are just soo many perverted men out there, SubhanAllaah and AstaghferAllaah.
SalaamualikumwerahmetAllaahewabarkatuh.