In language, both dysphemism and cacophemism are rough opposites of euphemism, meaning the usage of an intentionally harsh word or expression instead of a polite one.
The latter is generally used more often in the sense of something deliberately offensive, while the former can be either offensive or merely humorously deprecating. Examples of dysphemism include the American military's use of "shit on a shingle" for their common breakfast of creamed chipped beef on toast, or "dead tree edition" for the paper version of an online magazine.
Many of the same subjects can be dysphemized as euphemized, such as sex and death -- a well-thought-of dead person may be said to have "passed away", a disrespected one to have "kicked the bucket" or to be "worm food". Oddly, some humorous expressions can be both euphemistic and dysphemistic depending on context: for example "spank the monkey" might be used as either a softer alternative to "masturbate", or as a more deliberately provocative one depending on the audience.