Obviously the cock is the organ of the male body most effectively wired for pleasurable sensation, and there are huge stretches of the pleasure/pain boundary to be explored in its vicinity. But arguably more important is the psychological angle: for many men, cocks are the center of sexuality and a symbol of sexual potency and when someone helplessly undergoes abuse of his most precious appendage the psychological charge is immense. A site normally associated with indulgent pleasure is being transformed into a vulnerable target for punishment and pain. There are also clear links between CT and interests in sexual control and chastity.
Parts of the Penis and How to be Cruel to Them
Shaft - A structure of several layers, the core layer being spongy tissues (the corpora cavernosa) that engorge with blood during erection and the arteries that supply them. Within this and a little closer to the underside is the urethra (the duct that carries piss and spunk) and around it muscle fiber, nerves and minor blood vessels covered in a loose layer of skin. The shaft is the least sensitive part of the cock, though the sensitivity of the skin that covers it increases greatly when stretched during erection -- appropriately, because an erect cock, being under pressure, is far more fragile than a flaccid cock. The flaccid shaft can be struck with the palm of the hand, knuckles or objects like small 'cock-whips', rulers and beaters (though avoid excessive force - see below); squeezed with hands or otherwise pressurized with bindings; scratched and abraded with fingernails and rough-textured objects like stiff brushes; subjected to extremes of hot and cold (temperature play); pinched on the surface skin with fingers or clothespins and clamps. When erect similar treatments could be applied but much more gently. In both cases avoid too much pressure on the underside, where the urethra is closest to the surface.
Foreskin - The fold of skin that covers the glans when flaccid and should roll back to expose it on erection is basically skin with nerves and blood vessels, and a little more sensitive than the shaft, particularly on the inside. Even when it has been removed by circumcision for religious, health or cosmetic reasons, a remnant usually remains, particularly of the frenum, a web-like structure that attaches it under the glans and can be a very sensitive site for pinching and pegs. The foreskin as a whole can be squeezed, stretched and twisted fairly firmly to no real ill effect.
Glans (head) - Primarily spongy tissue (the corpus spongiosum, erectile but less so than the shaft) covered in a thin, tight and highly sensitive skin layer. The most sensitive part of the dick, even more so in many circumcised men, and particularly so at the ridge at its base, the corona. Little effort is needed to produce results, and some men find even gentle stroking difficult to bear. Can be struck like the shaft, squeezed, pinched, subjected to temperature play, rubbed and abraded and so on. Sometimes a little water-based lubricant helps things along.
Urethral opening or meatus (piss hole) - Often very sensitive and tender, particularly just inside, which in many people is an unexplored territory, and can be carefully teased with fingers or other objects such as cotton buds, lubricated if less discomfort is desired, and also stimulated by pulling and twisting on a healed Prince Albert piercing. However the urethra is sterile inside and any objects to be inserted more than a centimeter (0.5") or so should be sterile too. See Catheters and Sounds for more details of urethral play, which has its own potential dangers.
Special Techniques Cock And Ball Torture (CBT) Techniques
Much enjoyment can be gained by exploiting the cock's propensity to increase and decrease in size somewhat independently of the conscious control of its owner by various forms of cock bondage. One of the most common pieces of male SM wear is undoubtedly the cock ring, a metal or rubber ring (the latter are usually vacuum cleaner drive belts repackaged by fetish shops at a vast premium) through which first balls (one by one) then cock are slipped when flaccid and which can give a pleasantly constricted feeling when erect.
With some men, unfortunately, the difference in size between tumescense and detumesence is so large that it's impossible to find a size that stays on all the time but isn't dangerously tight and uncomfortable on erection. As David Stein recounts: "I once made the mistake of putting on a metal ring at home before going out. At the bar, when I lost my erection in a moment of distraction, the ring came off, slid down the leg of my jeans, hit the floor with a clang, and rolled away. Not the way to make a good impression." A variation on a ring is a simple cock strap that goes round the same site, often made of leather or neoprene and adjustable to size.
During a scene, the snugness of the bindings could be increased so that erections are deliberately made uncomfortable or painful (there are some hazards to this -- see below): with some people this can result in a particularly vicious circle with the discomfort itself exciting further erection. This can be achieved with cords, laces or thongs, for example tightly connecting loops around the glans with loops anchored round the base of cock and balls. A variety of purpose made cock straps is also available for the purpose, such as the 'anti-erect'. There are obvious links here to chastity techniques.
In addition, cocks are often the focus of specialist techniques including clothespins, electricity, piercing (temporary and permanent), pumping, and waxing.
Cock And Ball Torture (CBT) Health and Safety
Circulation Blockage - This is probably the biggest danger in cock play, as pain may not be a reliable indicator. Tissue that's deprived of blood eventually stops hurting -- which doesn't mean it's okay! It may be irreversibly damaged. Any binding is too tight if it cuts into the skin and causes bleeding. Any binding is on too long if it causes the cock or ballsac to become cold or numb, but the third typical sign of circulation problems in limbs that are bound -- loss of color -- is less reliable in this case. The cock and ball sac normally become engorged with blood during sexual arousal, turning reddish or purplish as a result, and up to a point genital bondage just helps that process along. Circulation could be dangerously impaired by tight bindings before there's much loss of color.
A better sign of impaired circulation is edema, or visible swelling, of soft tissue in the cock or scrotum below or around a binding. While such swelling isn't dangerous in itself (it will normally go down on its own after circulation resumes), whenever it occurs the bonds causing it should be loosened or removed as soon as possible in order to prevent damage. Avoid genital bindings that can't be removed easily even when there's swelling. Tie with a bow-knot or some other knot that will release easily if you pull on the ends -- and be sure to leave the ends long enough to get at. Keep blunt-tipped emergency medical technician's shears (scissors) available to cut bindings in an emergency. Don't use a metal cock ring that's tight when the cock you put it on is soft. It's going to be a lot tighter when that cock gets hard, and you won't be able to take it off until the cock softens again -- which might be a long wait if the ring has caused severe edema.
To sum up: A good rule of thumb is to loosen tight genital bindings enough to restore full circulation every 20 to 30 minutes even without any signs of a problem. And in no case should anything tighter than a comfortable ring or harness be left in place overnight or throughout an extended scene.
Retrograde ejaculation - If a man is forced to come while tightly bound around the genitals, the semen may be forced back down the urethra and reabsorbed into the body. Deliberate retrograde ejaculation is a practice of Tantric yoga, and although possibly uncomfortable, there doesn't seem to be any direct medical research on whether it is harmful. Evidence from vasectomies suggests frequent retrograde ejaculations might at worst lower sperm counts or generate antibodies to semen. An isolated incident should be nothing to worry about.
Other problems - Foreskins can be torn, and if circulation in them is cut off for very long, the tissue won't retract normally and could even die and slough off.
Be gentle with genital piercings: if you rip a ring out, you'll need medical help to repair the damage and avoid a nasty scar, infection, or worse. If a ring does tear out, use an ice pack and local pressure to stop the bleeding (see the First Aid Manual) until you can get to a doctor.
A fracture, when an erect penis is struck hard and "breaks" with a loud cracking noise, is an unlikely but potentially serious problem, a medical emergency that requires prompt treatment by a physician. As first aid on the way to the hospital, use ice packs to control bleeding. But if you avoid hard blows to a hard cock, you won't risk the problem in the first place.