"Never shake a girl's hand"

Adam was either a Junior or a Senior and he had a girl come over to the house to study or something. Anyway, I introduced myself and shook her hand. They went upstairs to study. After she left, Adam chastised me for shaking her hand. He seemed to think that was pretty stupid/lame. I was only in 7th Grade or so, so of course I thought "If Adam says it, it must be true." So for a while after that I never shook a girl's hand. I simply stood my distance, and waved when I introduced myself...Adam never told what I was supposed to instead of shaking hands.