Asshole (or arsehole in British English) is slang for the anus and can be used as a derisive descriptor of an unpleasant person. It is formed from arse, which according to the Oxford English Dictionary has been used since the 11th century to refer to the rump of an animal and since the 14th century to refer to a person's buttocks. The combined form arsehole is first attested from 1500 in its literal use to refer to the anus. The metaphorical use of the word to refer to the worst place in a region (e.g., "the arsehole of the world") is first attested in print in 1865; the use to refer to a contemptible person is first attested in 1933.Lighter, J.: Historical Dictionary of American Slang, Random House, 1994. But as with other vulgarities, these uses of the word may have been common in oral speech for some time before their first print appearances.
Semantics
The word is mainly used as a profanity towards someone the speaker does not like or whose behavior is hurtful, self-centered, or p