Tennis Buttock

It is no coincidence that the English verb to spank is the only one specifically meant for physical discipline of a specific part of the body, and various other languages have terms specifically referring to spanking; in many punitive traditions, the buttocks are the preferential target for painful lessons, from educational to judicial, as offering them for punishment (especially uncovered) adds a psychological dose of embarrassment and even sexual humiliation to the pain, which can be meted out with less risk of long term physical harm than elsewhere. There are, in various cultural traditions, expressions like "seat of learning" which refer to the preferential paining of the posterior in a submissively bent and exposed position.
Many comedians, writers and others rely on the buttocks in these and other ways (such as flatulence and toilet humor) as a source of amusement, camaraderie and fun, despite (or in some cases for the sake of) the risk of being in dubious taste, if not censored.
In the majority of modern cultures, the buttocks are rarely shown naked and are generally considered unsuitable for ornamental body markings and body modification. However, they may be preferential for discreet markings, such as secretive membership proof or to be shown in intimate company (e.g. amongst lovers).
In American English, phrases use the buttocks or synonyms (especially butt and ass) as a pars pro toto for a whole person, but generally with a negative connotation. For example, terminating an employee may be described as "firing his ass". One might say "move your ass" or "haul ass" (or the polite, understood euphemisms "move it" or "haul it") as an exhortation to greater haste or urgency. Expressed as a function of punishment, defeat or assault becomes "kicking one's ass". Such phrases also may suggest a person's characteristics, e.g. difficult people are termed "hard asses" (polite euphemism: "hard nosed"). People deemed excessively puritanical or proper may be termed "tight asses" (in Australia and New Zealand, "tight arse" refers to someone who is excessively miserly). An annoying person or any source of frustration may be termed "a pain in the arse" (euphemism: "a pain in the neck", though some claim that this alleged euphemism actually appeared in English earlier than the former). An incompetent or ignorant person is sometimes called a "dumbass", and an annoying person a "jackass".