If you are a person talking on your cellphone in public and I can hear you, I will be eavesdropping. Because I'm just nosy that way.
I catch people lying all the time. Like the woman at JFK in the bookstore with me. We'd checked in for the same flight, and now had lots of time to kill. Which explains why we were both standing around reading magazines we had no intention of buying. She answered her phone and started talking about nothing very interesting. But then she says, "OK, I gotta go, my flight is boarding now." And I look at her like seriously? It's not boarding for 45 more minutes. If we're lucky.
Or the guy sitting by me outside of Peet's. He was slumped in a chair, his head back, staring at the sky while he talked on his cell.
Guy: I already told you.
pause
Guy: NOTHING HAPPENED WITH HER.
pause
Guy: Well, she's lying.
pause
Guy: (sighs loudly) I don't know.
pause
Guy: I have to go. My battery is running out.
pause
Guy: My battery is RUNNING OUT. I'll call you later. Bye.
He then dials another number and talks to his buddy about sports for the next 15 minutes.
Speaking of eavesdropping, my best one ever was a few years ago at a swanky restaurant. A man and a woman were sitting at a table close by. They started out having a romantic dinner but it began to death spiral during the entree. I was straining to hear because oh my god, it was obviously so juicy but they were whispering through clenched teeth, which is especially hard to decipher. Finally, the woman pushed back her chair and said, with exceptional clarity, "John, you're the one who came home with the disease!" and walked out of the restaurant.