More dirty sock
After my mom asked me to jack off in a sock I noticed that more often she would 'catch' me dressing, showering and changing clothes. She always said sorry, and kept on talking. So I made opportunities for her. I would call her from the bath, asking after leaving a towel a few times in my adjoining room, if she would get it for me.
Then I would dry in front of her and think of things to talk to her about. I always left my room door open, and more than once masturbated when I knew she would catch me. There were even a few times that I 'forgot' to get a sock to come in so I would call her, asking her to get one for me so I wouldn't have to stop to find one from the laundry room.