Answer:
not talking
Explanation:
weak social behavior is not talking or being by yourself
I believe teens definitely are most concerned about muscular strength. They are more worried about that because they want to protect themselves, impress others, sometimes kids just want to bulk up to not look so wimpy, etc.
I would have to say teens are less worried about flexibility because when you have mussels why worry about doing the splits or putting your leg up to your head. One thing will always distract you from the rest.