I find you reclining on the bed, maybe looking at your phone, but you put it down and look up at me as I come closer. I just got back from work and am still dressed for it--a red turtleneck and a black knee-length skirt and leggings--while you're just laying there in a t-shirt without even underwear on, your cock hanging out loose between your spread legs.
"Is this an invitation?" I ask, but before waiting for a response, I get down on my knees next to you and take your cock in my left hand while reaching under it to try to find your balls with my right. Because of the way they're hanging loose beneath you, I can't see them initially, and wonder how small they are, but when I find them I'm pleased to discover that they are actually quite large and plump, even though they're hanging loose and low.
I kiss your foreskin-covered glans and then reach under your shirt with my left to rub your stomach and nipples while I continue manipulating your balls with my right. When you start to reach down to touch your cock yourself, though, I say "No." firmly while grabbing your arm with my left hand and pulling down on your balls hard with my right.
You start to say that you just wanted to pull back your foreskin and rub your frenulum while I play with you, and I have to remind you, "You know the rules. First, your foreskin is to keep your glans fully covered at all times unless I give you specific permission to retract it, or do so myself. Second, when I'm playing with you, you aren't to touch yourself at all: you're mine, and that means your body is mine to handle as I see fit."
You murmur out a soft "Yes, Miss." and I release your balls. I get up and open the drawer where I keep the ropes for tying you up, and I pick out four short lengths. I begin to tie each of your wrists and ankles to a corner of the bed frame as I continue, "These rules are for your own good, you know. When I found you, you were such an obsessed stroker-boy, constantly playing with your nice, big cock to the point you couldn't focus on your work, or on pleasing a partner."
"Some Mistresses probably would've had you circumcised really tightly, so you couldn't get as much pleasure from masturbating. But I recognized that you have a wonderful foreskin, and I wouldn't want any harm to come to it."
"So, instead, I decided to use your foreskin as a sort of chastity rule: you're never allowed to retract it without permission. After all, you're a horny, big-dicked boy, not a woman with a nice, proper little girldick like I have that stays out of the way unless I get aroused. You need a reminder to keep you from touching your cock all the time, and having your foreskin in place is a good reminder."
With that, I finish the last knot and you stare up at me and whimper a little as you lay spread-eagle on the bed. I kneel at the bedside and return to my previous position, with my left hand reaching for your nipples under your shirt while my right hand grabs hold of your balls and tugs down on them. I place my thumb and pinky on your nipples and start to press down, while my fingertips begin to press into your scrotum and massage the base of your penis through the skin.