I would make the comment that "I've noticed you park down the street but feel free to use my driveway." I have a teacher who knocks with a feather. She always knocked lightly and then peeks in the window as if she knows I wouldn't have heard her and she can watch while standing there. I've told her she needs to knock louder but she won't. It pisses me off too so I know how you feel. I'd rather she just look in the window and watch all she wants, then knock loudly.