I haven't found too many people who think people watching is a bore. Think about going to the mall, the airport, concerts...you name it. There is always an opportunity to people watch.
For an author, people watching is a must for character development. Every person on this planet, and other planets for that matter, are distinctly different. We all talk different. We have our own walk. Some of us exude confidence, sexuality, and poise. Others clearly are standoffish, lazy, or meek.
It's no secret you can bury your personality by just how you walk. Did you know that Marilyn Monroe could walk down the street and not be recognized? She had that keen sense of herself. She could actually turn on her sexuality and stop traffic. Or, she could walk like an average woman, her mind filled with grocery lists and chores, and never be noticed.
I've more than once sat at a table with my husband or a friend and watched someone. In my head I'm making their story. Some people are transparent and what they show you is who they are. Others, you can tell there is a mask. And if you watch people as intently as an author, you'll begin to see it.
As an author, keen on watching the world interact, I keep a data base of items in my head. And also like many authors, I'm one to sit at my computer and make faces, hand gestures, and I murmur to myself trying to bring that certain character to life.
People often ask if my characters are based on any one person. If they are then they are acknowledged in the front of the book. But even then they are based on characteristics of the person, and perhaps not on the person as a whole.
My characters are based on that man that walked down the street with his phone to his ear. His dodging pedestrians in an offensive football move as he made his way from his office to the food cart on the street. Others are based on mothers who either have control over their three small kids, or who seem to, but you can see that crease between their brows as they try to keep a hand on the situation that changes from second to second.
Character development is all around us. It's not hard to come up with the next person to put into your books. Keep your eyes open. They are out there...everywhere.