Receive every man with joy

Rabbi Ishmael would say: ... and receive every man with joy.

Rabbi Matya the son of Charash would say: Be first to greet every man.

When you frown at other people, you rob them of their happiness. They ask themselves, "What did I do wrong? Why is he or she mad at me?", and they lose confidence.
http://lazerbrody.typepad.com/lazer_beams/2010/05/frowns-and-smiles.html

This past Shabbos, I attended a Pirkei Avot shiur. As I was approaching the entrance, I recognized a woman and wished her a cheery good Shabbos. She responded "hi" in a pretty somber tone and I felt like a glass of cold water had been splashed on my face.
I reminded myself that this woman was a naturally quiet and shy woman and I shouldn't be upset that her greeting wasn't more effusive.
The opening words the Rabbi offered at the shiur were about being the first to greet every person. I assumed that the Rabbi would launch into a shiur about the importance of saying hello to people that one meets, and I thought that the topic was an important one for our community.
Yesterday afternoon, I was walking on the street and came upon a woman I didn't know. Recognizing a fellow yid, she smiled broadly and greeted me with a "hello." My mouth immediately curved into a smile and I responded in kind. I was left with a warm feeling.