Walked in on my son masturbating

As the title says. But he was doing it in the kitchen. When he was meant to be washing dishes. With the light on. In full view of anyone who looked through the window. Or -like me- walked in the kitchen. He's 12. I mean I know it was going to be happening, but why do it in a place he's so likely to be caught out? How do I even begin to talk to him about this. I'm mortified. He's mortified. Any advice appreciated. via /r/Parenting http://bit.ly/2G6HAuf