When my girlfriend and I know that I have been very naughty and deserve her strict discipline, I am sent to our bedroom with instructions to, "... be naked by the time I get there!"
When she arrives, I'm laying face-up on our bed, so that she can immediately see whether or not I have an erection, which is against her rules when I am to be disciplined. But, of course, I always do have an erection. Before using her hairbrush paddle, her leather strap, and/or a hickory switch on my bare bottom, she uses a school ruler and/or a very short/thin leather strap to discipline my "naughty penis" (she calls these her "penis paddle" and her "penis whip").
I love when she uses these implements to enforce her rule that I, "... shall not have erections without permission". She starts out with slow/tender slaps, which are incredibly pleasurable, but quickly ramps up intensity until she beats down my sexual arousal. She does this because she knows that when my sexual arousal has been tamed, I will NOT AT ALL enjoy the butt-blistering that she will give me next.
Sometimes, my erection will start to return when she starts to tan my butt. If this happens, she she puts me back on my back and starts over with her "penis paddle" and/or "penis whip".
Sometimes, she will intentionally discpline my naughty penis in such a way as to cause an orgasm. These are some of my most powerful/enjoyable orgasms, which she allows, because she knows that after an orgasm, I can quickly be brought to truly repentant tears when she goes to work on my butt.