Well GZ also has a lengthy history that includes domestic violence, attacking a female security guard, violence against a police officer etc. Zimmerman also has documented history of lying in a court of law.

Sure, calling the police is not illegal but he was advised by the 911 dispatcher not to follow Trayvon Martin and seems to have a history of looking for trouble. Also, It's not illegal to walk home with a pack of skittles in your pocket. 

As for how the friend on the witness stand acted, I suppose there are worse things she could do such as shooting an unarmed person who was walking home minding his own business.