I´ll copypaste this Quora answer by the very John Fessée, Writer of the popular blog goodboyspankings on blogspot:
"Making a spanking humiliating for any particular person means that you have to focus on what that person finds humiliating. If someone is fastidiously clean, they need to be shown to be dirty, for instance. For a teenager, it means you need to play off their fears and especially those fears surrounding body image, social acceptance, and their likely very confusing sexuality. Remember that embarrassment is the psychological feeling of wanting to hide a fault or trait. Humiliation is the sociological experience of having others notice, comment or otherwise negatively draw attention to real or imagined faults, traits or characteristics. In all of this, one needs to be subtle. The spanking is the direct assault; the humiliation is a glancing blow. Think of that time when someone pointed out a stain on your shirt after you spilled on yourself at lunch. Their intent was merely to comment on a fact or perhaps be helpful but you internalized the message to mean that your were clumsy and unkempt. Let the imagination run.
That said, a teenager is going to be very body conscious so, of course, they should be naked. My favorite justification for nudity is that the spanking ritual is about purification of revealed sins where sin is the body revealed when clothes are removed. Few comments are required. Perhaps a, “you look so grown up,” or “wouldn’t think we would have to spank someone so grown up anymore.” Really, all that is needed is to let the eyes linger on key body parts for just a moment too long. Playing off the teenage fears of being socially damaged is frighteningly easy. The mere fear that what is happening would be found out is enough. The spanking should involve a lengthy ritual involving being paraded naked through the home to the place of punishment that is far from the most private location. There should be constant fear of not just the spanking itself but that it might not remain a secret. The longer the ritual (go get undressed and come back, let me finish this chore, fetch the spoon, stand in the corner and think about what you did,…) the more opportunity for discovery and the more humiliating the experience. Lastly, one does not have to sexually assault the teenager to play off their insecurities around their sexuality. Anyone that has passed through puberty will be conflicted about their genitalia and erogenous zones. The goal here is to merely toy with that confusion.
Keep the genitals displayed as much as possible and when they aren’t displayed, allow for stimulation with the careful placement of pillows, towels, arm rests, or other objects against which the young person can possibly grind. Then, it comes down to merely commenting, “enjoying this, I see,” followed by a few prudish tsk-tsk sounds. It is, of course, a trap. Remember first that spanking will create blood flow to the buttocks and genitals causing reactions similar to those of arousal and which, conveniently, can facilitate arousal (and erect penis is more sensitive than when flaccid, for instance). Spank more gently when you suspect that the teenager is being stimulated so that they can experience arousal. Then, call attention to that and redouble your spanking efforts as you feign anger and disappointment. If male, reposition them after they achieve an erection so that it is prominently visible (standing, bent over a counter, on back/legs up diaper position). Young women are trickier but there are more subtle signs of arousal: lubrication, clitoral/nipple erection, vocalizations. However, regardless of whether there is or isn’t arousal doesn’t entirely matter; ask if there is or speculate that she is aroused regardless. The idea here is that you want the teenager to have a sexual experience but you want to pretend that it is inappropriate and that you completely didn’t intend for them to feel that way. The ultimate humiliation would be if they achieved an orgasm during the spanking but it is enough that after the spanking, they be given some time alone in private to satisfy their erotic needs. In other words, any time a teenager is spanked, an orgasm should occur during or shortly after it happens.
I feel that the strong sexual response should itself not be punished unless the orgasm or ejaculation occurs during the spanking in which case, the spanker should again feign disgust, disappointment, and anger as an excuse to spank harder and faster, you know, because he made mess or wasn’t appreciating the spanking. Be sexually positive but perhaps judgmental about time, place, and context. Comments like, “glad we got that out of the way,” “maybe now you will appreciate your spanking,” or “oh, what a mess,” cut to the bone. Add a little ritual around cleaning up after an accident or preparing for one “just in case”. All of this, of course, will definitely traumatize a teenager. Much of it is part of the storyline behind my spanking fetish not because any of this happened to me but because I was and am deathly afraid of this or the non-spanking/nudity/sexuality equivalent."
https://www.quora.com/What-kind-of-position-can-a-teenager-get-humiliation-by-spanking