Why does this man treat me like this in front of his friends?

I have been seeing a 38 year old divorcee for several months. When it's just us, he is respectful and very attentive. However, when we went out with his friends yesterday, he repeatedly tried to grab my in front of them. He also made a reference about his friend not setting him up with his "hot" sister. He acted totally unlike himself, and I feel very confused. Later in the day, he calmed down and began acting more like the man I knew, but really do not understand this bizarre behavior.