Context #1:
Joe: I have to pick up my friend today at the airport. I hate going to the airport.
Chuck: Really? Not me! I love sitting in airports. It's a great place to people watch!
Joe: Yeah I guess that's true.
Context #2:
Sally: I went Christmas shopping at the mall last night. It was so crowded! There were way too many people.
Bill: Yeah, I know. Every year before Christmas the mall is a zoo. I let me wife do the shopping while I find a comfortable place to just sit and do a little people watching. There are so many interesting things to observe.
Meaning: "to people watch" is an expression used to describe the activity of just watching the different kinds of people in a public place. Usually someone "people watches" just out of curiosity. This idiom can be found in the book LSI Speaking Transitions. This book is used to teach Level 4 Speaking/Listening at LSI schools. For more information visit:idiomstudy.blogspot.com