It really pays to be kind to others. We don't know what a person is going through at a time. A little empathy, a little kindness or respect will help - or might go a long way. Or, it might save us from embarrassment.
A stranger you meet in a bus or train could be your future employer or landlord or neighbor or in-law or could be one of your relatives like 3rd or 4th degree of consanguinity that you just happen not to know.
One episode of "Be Careful with my Heart" came into mind. Maya (Jodi Sta. Maria), the main female character, saved the mute child Abby (Mutya Orquia) when she accidentally entered into the airport's luggage counter and passed through the screening. Maya covered Abby with her own body to shield her from possible harm. Abby is not in any way related to Maya but it did not hinder Maya to reach out to an innocent child. Later on in the story, Maya is hired as Abby's governess by Sir Chief (Richard Yap), the lead male character who plays the role as Abby's father. And the story goes on...
The incident in this fictional story is not far from our daily lives. I think the story was inspired by real life events. There is still some Good Samaritan in this world like Maya. I'm one of the many who can attest to that having experienced this blessing several times already. On some occasions, I was given the opportunity to be a 'good neighbor'. In these opportunities, most of the time, whenever I do a little help, it bounce back at me. Just like the saying: what goes around comes around, what goes up must come down. Since what I did was good, it goes back to me in another form; though, still good. Good karma you might say.
However, it's inevitable that at some point we show less kindness to a person because of a reason (probably) of greater gravity, though. I think it's normal. Self-respect, self-preservation or emotional or physical security precaution, whatever reason a person may have for acting not-so-kindly sometimes, is just normal. But bear in mind to take it in moderation (yes, like alcohol, drink moderately) so you don't become the kontrabida (villain) in your own story. :-)