He asked them to keep it down because he had some studying to do but couldn't resist going to the bathroom and staring at Blondie through the window. He started fantasizing about getting his mitts all over her bodacious body and having his way with her. He started jerking off to all those images flooding his mind. Blondie unwittingly walked in on him and caught him with his dick in his hand. Maybe next time all the embarrassment he felt will remind him to make sure the door is locked.