I'm going to ignore someone at the bus station
Why do you want to ignore someone at the bus station?
I don't care about this person, they are not worth my time.
It is mean to  ignore someone just because they serve no purpose to you. You should at least acknowledge someone if they are being polite to you.
Why does it even matter, people can ignore others if they feel like it.
Ignoring others is a bit rude. Just say hello back, and move on with your day. Someone trying to be friendly should not be met with resistance.