Good morning/afternoon/evening, depending on where you are at the moment.
Sometimes, I think social media has translated into a relaxing of standards. For example, if you see someone you know on the street and they say Hello or wave, you wave or say Hello back. It's common courtesy. I admit to doing this on occasion, not responding when someone toots a greeting at me, and I'll try to do better. Everyone wants to be seen and acknowledged when they go out of their way to greet. ❤️