Turning your shock into decisiveness for an idea that’s just come out of this situation.
"Woah, uh miss you might wanna-" the teen boy fumbles on his words, pointing at your glistening breasts. He grabbed the top out of the water before handing it you. As you put it back on, you bring his hand to touch your breasts as the top once again covers your modesty - his hand was now dumbfoundedly squeezing your right breast as it was snaked under your shirt.
"You can feel them!" You laugh at the the expression of shock on his face.
He was clearly not paying attention to your face, paying close attention in exploring every nook and cranny of your boobs with his hand.