Call him out on it
From Create Your Own Story
A blush slowly creeps into his face as you point his obvious erection.
"I...I...um...."
"It's alright, it happens"
"I...I'm sorry, I haven't had a chance to take care of it in awhile"
You both look at each other awkwardly before you look back at his crotch. You know he knows that you're staring, but you don't care; his bulge is too enticing to look away. As you stare it starts to get bigger and your eyes widen in surprise. You knew he was big, but you never really knew just how big until now. You can't resist touching him; you need to feel his massive colum of flesh in your hand. Your hand darts down to fondle his crotch and you look back up to see his reaction. The plain shock on his face is enough to make you worry he'll reject you. Luckily for you however, he doesn't even try to stop you as you rub his crotch.