There are numerous examples of such practices. For instance, more recently in the summer of 2011, people in a Fairfax shopping mall (Virginia, USA) were terrorized by someone the press dubbed the ‘Serial Butt Stabber’ and the ‘Butt Slasher’ (a man who repeatedly stabbed females on their bottoms through their clothes). One online article noted that:

“The so-called butt-slasher has been pricking women in the rear end with sharp objects, in malls in Fairfax Virginia. Six women have reported being victimized so far, shopping at T.J. Maxx, and another 18-year old at a Forever XXI store, who felt a ‘sharp pain” and believed a hanger had stuck her, though she noticed a man binding down to pick up clothes supposedly fallen off a rack”

Dr. Anil Aggrawal in his book Forensic and Medico-legal Aspects of Sexual Crimes and Unusual Sexual Practices, defines piquerism as sexual arousal from penetrating another person’s body with sharp objects (such as pins, razors, knives, etc.). Other definitions on various online websites define it as “sexual excitement from stabbing/blood letting” (which in my opinion, and based on more academic writings, is too wide ranging to be clinically useful). The Wikipedia definition (which appears to have been based on that found in M.S. Davis’ 2002 book The Concise Dictionary of Crime and Justice) notes that:

“Piquerism or picquerism (from the French piquer - "to prick") is sexual interest penetrating the skin of another person, sometimes serious enough to cause death. Piquerism is a paraphilia and form of sadism. The most frequently targeted areas of the body are the breasts, buttocks, or groin”.

Given the relatively regular incidence of piquerism in the popular media, I was quite surprised to find next to nothing academically. There are passing references to piquerism in the clinical and forensic science literature but nothing (as far as I could find) on the prevalence or etiology of the disorder. Dr. Wade Myers has a short section on piquerism in his 2002 book Juvenile Sexual Homicide. In one of the chapters, Myers recounted the case of two teenage murderers (‘Frank’ and ‘Andy’) who killed and mutilated a pregnant teenage girl they had both previously had a sexual relationship with. As Myers wrote:  Regardless of who first came up with the idea of the murder, [Frank and Andy] took her to a remote area in some nearby woods. Andy first had consensual sex with the girl. When Frank approached her for sex, she rebuffed his advances. The attack on the girl started after this interaction. Each of the boys attributed the cascade of murderous actions to the other. The victim was initially choked manually and strangled with a radio cord. Unconscious, she was carried further into the woods. She regained consciousness and attempted to run. She was bludgeoned with a piece of lumber, a tree branch and a concrete block. The bludgeoning with the concrete block…detached part of the scalp. One of the boys tried to cut her throat with a knife, and her arm revealed defensive wounds from trying to protect herself during the knife attack”.

The medical examiner reported that the girl had been repeatedly stabbed and that the boys had done it for the “heck of it”. Dr. Myers claimed that offender behavior was “an expression of the perversion known as piquerism”. Dr. Myers admitted he knew little about piquerism (and wrote “little is known about piquerism in adults, and even less so in children”), so he contacted Dr. Richard Walters (Omega Crime Assessment Group, and former prison psychologist for the Michegan Department of Corrections). Based on his colleagues’ expertise, Dr. Wade subsequently noted:

“Piquerism is sometimes performed post-mortem. It generally refers to the penetration of human flesh, although it is sometimes practiced against animals. The piquer’s range of activities for sating his or her needs can be a purposeful single prick with a pin or knife, multiple stab wounds to an eroticized area, or elaborate cutting, stabbing, biting and mutilation of a victim. Piquerism becomes part of the repertoire of many sadists, depending on their progress along the ‘sadistic learning curve’. Often the sexual mechanisms inherent in piquerism are ignored during the assessment of sexually sadistic crimes. The prevalence rate of piquerism is unknown”.

Many authors note the link between piquerism and sexual sadism. In an online article on sexual sadism. Dr Stephen Hucker reviewed the characteristics and predominate features of what he described as “major sexual sadism”. 
Dr. Hucker noted that this type of sexual sadism was typically non-consensual and usually culminates in major injury or death. He also noted the types of behaviour that accompanied major sexual sadism as including: (i) severe beatings, (ii) torture, (iii) burning and cutting, (iv) stabbing in the breast or buttocks (piquerism), (v) rape, (vi), murder, (vii) vampirism, and (viii) necrophilia. This is also confirmed by Dr. Anil Aggrawal in his 2011 book Necrophilia: Forensic and Medico-legal Aspects, where he examines lust murders:

“Lust murders are homicides in which the offender stabs, cuts, pierces, or mutilates the sexual regions or organs of the victim’s body. The sexual mutilation of the victim may include evisceration, piquerism, displacement of the genitalia in both males and females, and the removal of the breasts in a female victim (defeminization). It also includes activities such as ‘posing’ and ‘propping’ of the body, the insertion of objects into the body cavities, anthropophagy (consumption of blood and/or flesh), and necrophilia”.

A particularly gruesome case involving piquerism was described by Vernon Geberth (former Commander, Bronx Homicide, NYPD) in an article ‘The Anatomy of Lust Murder’ in a 1998 issue of Law and Order magazine. He wrote:

“The two victims were a mother and her fourteen-year-old daughter  …Once his victims were unconscious and dead he engaged in hours of sexual deviance with their bodies. His intention was to knockout the fourteen-year-old and then torture her to death. However, he had hit her with such force that she died. He eviscerated both of his victims. He had sex with their corpses and drank their blood before posing and propping them with their body parts and inserting a baseball bat into the daughter's vagina. He removed the breasts from the mother and placed them in the bedroom on end tables on either side of the bed where the daughter's body was found. He incised the skin of the pubis from the mother and placed the tissue into her mouth. He incised the skin of the pubis from the daughter's body and placed it upon the right side of her face. He then engaged in postmortem piquerism by stabbing into the daughter's throat a total of sixteen times…His admitted fantasy was to torture and kill young girls as another male anally sodomized him. All of the cutting, mutilation and overkill type wound structures were directed towards those parts of the body that the offender found sexually significant to him and these activities served as his sexual stimulus. 

The piquerism inflicted on the body of the sixteen-year-old was substitutive for his "torture" fantasy”.

A number of infamous murderers are known to have carried out major acts of piquerism. Arguably the most infamous was Jack the Ripper. A paper by Dr. Robert Keppel and his colleagues in a 2005 issue of the Journal of Investigative Psychology and Offender Profiling concluded that “the injuries sustained by the victims displayed the signature characteristic of piquerism”. The Russian mass murderer Andrei Chikatilo (‘The Butcher of Rostov’) was known to be impotent but derived sexual satisfaction from stabbing and cutting his many victims. American serial killer Albert Fish (also known as ‘The Brooklyn Vampire’ and ‘The Moon Maniac’ amongst many other names) was known to have engaged in piquerism with many of his victims (and also had a penchant for self-piquerism – particularly the sticking of pins into himself).

The reasons as to how and why people engage in piquerism have yet to be researched in any depth. Most of the theorizing is speculative at best. The Freudian psychologist Dr. Judy Kuriansky in an online essay entitled ‘Piquersim Pervert’ (and in direct reaction to the mall ‘butt slasher’ in Fairfax Virginia) speculated that:

“His proclivity was an attack on the butt. A boy can be subjected to a mother taunting him, ‘you’re a bad boy’ and going to be punished and then giving him a rear end beating, which is sexually stimulating. He then associates being attacked on the rear with sexual turn-on. Add to this, that he gets satisfaction from mother’s attention, albeit negative. And he comes very angry at her, which explains how he then projects his punishment urges onto women. Such a paraphiliac perversion also means that the man is incapable of a healthy relationship with a real woman, and can only focus on a body part. The perversion can also come from being beaten by the father with a belt to the point of drawing blood. There is always a danger that such a paraphiliac already acting on aggressive urges can become a lust murderer”.

In an online article entitled ‘Explaining Mutilation and Piquerism’, the anonymous author notes that the motives behind piquerism mutilation of female victims still remain a mystery. The author claims that piquerism acts are:

“…largely perpetrated by angry heterosexual males on females or homosexual males on males – in other words, an act directed by males onto the object of their sexual desire…The preference to use a knife for mutilating a victim beyond what is necessary to kill is called piquerism. The killer expresses his sexuality by penetration the victim with a knife. The victim’s screams, the bloodletting, and the odors all create for the murderer a harmonic sexual experience. Some killer’s ejaculate uncontrollably without touching their genitals as they stab or hack at their victims. Some experts associate piquerism with cultural construction of femininity, with its association with the body, bleeding, birth, which link women with a mortality that provokes a dual reaction: anxious fear accompanied by erotic desire. If the duality slips out of control, the consequences can be horrific”.

Perhaps the most parsimonious explanation of piquerism is a quote from the fictional character George Huang, an FBI psychiatrist in Law and Order: Special Victims Unit. In Episode 2.20 (called ‘Pique’), the head of personnel at a software company is found raped and stabbed to death. In court, Huang simply says:

"He suffers from piquerism, counselor. The knife represents his penis. It is not disposable"

References and further reading

Aggrawal A. (2009). Forensic

http://www.psychologytoday.com/blog/in-excess/201501/life-knife-edge