We shall first focus on male Klingons with female Klingons, to give you an idea on how the system is supposed to work.
It is often hinted at that the forhead isn't the only place that Klingons have ridges. Which is true. The Klingon penis is covered with ridges. It is a very strong and ridged organ, necessary to obtain access to the female Klingon's guarded insides. What isn't known is that it opens. After the male has inserted himself into the female and enough stimulation and preasure is applied, the Klingon penis opens up, much like a terran bannana. It has a slit down the middle, and the two sides curl around revealing an ultra-sensitive inner-penis. Now when the "nagh DIr" peels off, it's two ends are pointed, and they curl back and dig into the woman's walls. The female Klingon's body is designed for this, it "allows" the male to penatrate these walls, but not all at once. The more aroused the male becomes, and the further into the mating act the two are, the deeper these "pachDu'" dig into the woman. And the deeper they dig, the more pleasure the woman recieves. It should be noted though that at this time, it is not possible for the male to remove himself from the female; doing so would cause severe damage, ripping the females flesh away. However, it would take incredable force from the male to get away in such a manner, not that anyone would try, it is not honorable to "pull-out". After the Klingon male has climaxed, the "pachDu'" slowly retract back into place and the male is able to remove himself from his mate. Even though he is attached to his companion, he is still able to thrust back and forth.
Some Klingon women have a reputation of mating with their nujDu'. This takes a speacial skill on the females part. First, she must place enough pressure with her jaw muscles to open up her mate, and she must also be able to pull away to allow him to open up, giving her free reign with his inner-organ. Even though these be'pu' do not keep the pachDu' in their nujDu', they are often referred to as "being bitten on both sides of the cheek".
Mentioned earlier was the fact that the female's insides where guarded. It takes something very strong and sturdy to enter one of these ladies, their vaginas are covered by strong muscles, which both keep unworthy males from mating with them, and apply enough pressure to open up their mate's organ. Because of this, Klingon women cannot be "fingered" or "eaten out" like a Human woman. Another interesting fact about the female's anotomy is that upon climaxing, which Klingon women do often, every muscle in their reproductive system clynches down with extreme force, which in turn, gives their mate even more pleasure. It should be noted here that when Klingons mate they do it in a manner that Terrans refer to as "doggy-style". "Missionary-style" as some call it, is considered "weak". Anyone can thrust a woman onto her back. But for her to place herself in a matting position and allow the male to come up from behind her shows great trust on her part, and honor on the part of the man.
As one can infer, most Human women cannot endure a Klingon's sexual pachDu' digging into their vaginal walls. And it is a big let-down to the Klingon male to not have such a powerful orgasm from their mate, or to have their mate not powerfull enough to open them up.
Along the same lines, assuming a Human male could gain access to a Klingon woman, her orgasm could prevent him from any further mating practices, for life.
Yet, there are those Humans, both male and female, that have rich sexual lives with their Klingon mates.
tlhIngan loDpu' be'pu' je