Why does he aim for the middle?

Remember, we've already thrown modesty out the window. Our house is set up where there is a bathroom upstairs in between our room and Boy's room. This is the bathroom I shower in. It's pretty private, so I don't always take the best care in covering myself up in between the bathroom and my bedroom where I get dressed after a shower. I used to wear the towel around my waist but I'm not consistently responsible. I wouldn't hang the towel up back in the bathroom after I was finished getting ready. Apparently, Mommy doesn't "appreciate" picking up after me. So I adapt. I walk in "God's vision of man" back to the bedroom. Out of nowhere Boy comes bursting in. "I'm going to bang your bum! I'm going to bang your bum!" he screams and tries to slap me on the ass. I'm not the quickest in the morning and sometimes he gets me. It's all in good fun, but he doesn't aim for the meaty cheek. He aims for the middle. That's just uncomfortable. I guess when you think about it, the line acts as a target.