See Talmud Bavli 62, that Rav Chisda would be Makdim sholom even to a non-Jew.
Rav Moshe Feinstein ZT”L used to tell everyone good morning, even non-Jews.
The Lubavitcher Rebee ZT”L used to say good morning to anyone he met in the street, even women. (I heard this from someone who constantly saw this.)
The word “hello” can change someones entire mood or attitude.