What is the relationship between “catching” a yawn and social behavior?

Humans are hardwired to do what we see, hence the term, monkey see, monkey do. The relationship between “catching” a yawn and social behavior is that we subconsciously “catch” the yawn to be seen as “normal” because it is what someone around us has done. A lot of it goes back to psychology. I would suggest looking up Solomon Asch’s human conformity experiment to get a better understanding. :)