There was a video I used to jerk off too with a master training a young slave.
It was in a hotel/motel room, very amateur, and while the chubby young guy was learning to take cock, the master would kick him in the balls. Also the slave was wearing some sort of mask.
At one point, his whimpers tuned into real crying and he just got up and said he cannot take it anymore. Got dressed and went home. And the master was mocking him like 'oh, run to mommy!'
Unfortunately, I cannot find it anymore... Anyone have any idea?