Not very careful.
I have a nude photo of my BFF standing naked on the cottage deck which is on my lock screen. The screen lights up whenever I move my phone or a receive a text. I make it a point to ensure the random dude at the cash or at the restaurant see the lock screen. My BFF says she's embarrassed others see her naked photos but she's never asked me to remove it. Best is when she's with me at the restaurant. The waiter looks down at my phone then stares at my BFF. There have been a few waiters that have given us exceptional service and commented to her that she has a great body.