My rule of thumb (and it's mine - so not right, not wrong) is this:
If I think a person is mad-dogging someone. I tend to engage the person being looked at. If they don't want to talk that's fine and I'll go quiet. If a person is actually insulting/threatening a person, I speak up. If there is an act of violence, I assess. I am not a fighter and 5'2. I am not going to put myself where I become the victim to violence, but I will call for help and do what I can.
Is this right for everyone? No. It's not.
I can't just judge a look because I don't know what the person is thinking. What if the person is the ex of the other and the relationship is being rubbed in their face? What if they said something insulting?
What I am saying is that all the corruption and all the violation of civil rights comes down to 'not me' and good people doing nothing. I am not in a large demographic that is targeted beyond my gender which is bad enough. However, just because I'm not in that demographic doesn't mean I don't use my voice to help them. Not to start 'that argument' but there is white privilege and there is hetero privilege. If you don't believe in either, maybe you don't live in the US. I have never heard something stupid referred to as 'that's so hetero'. So while I cannot change the course of this overnight, I can use what voice I have to speak for those that cannot. People will listen more to me because I was born with blue eyes, pale skin and blonde hair. So when I talk, I make it a point that my words are to empower those that are being pushed down by the rights I received (and they did not) merely because of birth.
IF we all started just being good to each other, there would be so much more grace and love around us. You get what you sow. I say hi to everyone on a bus I sit by. I respect if they want their silence, but what if they hadn't talked to someone and they just need a hello or a smile? Is that too much time to take from my iphone game or the music in my ears? If they want to engage in conversation, I'll respect that too. We might learn that we are not an island in a sea of people, but we are social beings in a society of strangers that need not be so strange to us.
If more people spoke up because it's wrong to deny civil rights to a part of the population based on things they have no control over, maybe there wouldn't be hate crimes. Maybe people would not be afraid to admit who they are inside and allow it to reflect on the outside.
TL;DR - Make love not war -- Also No, I am never going to stand by and agree with someone that we should do nothing because it 'doesn't concern us'. If it involves another person being hurt or repressed; it damn well SHOULD concern us. If it doesn't, it might soon also be us.
Steps off her soapbox - sorry